Lackadaisy - THANK YOU!!!! There is so much good information in your posts, I feel like it should be a sticky for the Featherweights.
I don't love shopping - it's more like a necessary evil - so I never would have thought about plain old consignment shops. And I know we have a Filene's Basement here in Atlanta, but I've never been. I needto check it out.
And I can't wait to look at those websites and get some ideas for things to wear. One of the more annoying factors here is that, besides being generally fashion-challenged, I also don't know what looks good on my new, alien body. So I have to try everything on at the moment. But combining online with in person shopping sounds like a great plan.
If you ever want an unpaid position as my personal shopper, just let me know!
Everybody's offered you some great advice, and I'll throw in a couple of other options/reinforce earlier suggestions.
If you have an outlet mall near you--not just a regular mall, but one with designer stores at off-season prices--I cannot recommend Calvin Klein enough. Professional, wide range of styles and sizes, and classic. That stuff will live on for a long time as staples in your wardrobe, and the quality is so good you'll get a LOT of use out of it.
Also, Old Navy in the stores seems more juniors-y in terms of styles, but online they have a lot more professional staples: good basic pants going all the way to size 0 in some cases, sweater sets, and basic tees and tanks in cheap enough price ranges that the lack of quality means you can buy these in bulk.
Finally, Bluefly is another awesome option. I splurge on their stuff more for fancy dress things, but you can find reasonable options in normal daily wear stuff, too.
Haha, I'm happy to help! Obviously, I love clothes a bit too much... right now I'm still shopping my own closet, but I plan to be hitting up one of my favorite consignment shops next week for jackets and accessories.
On that note, I'm so glad you have a Filene's nearby! It's hard to score good, cheap basics online especially since you can't tell what the quality is (and I never buy knits/tees consigned because of the wear problem), but Filene's Basement is AMAZING for basics. At mine, the rows of tees are sorted by color, cut, and size so all you need to do is find your section, decide your price point, and then you can pick your favorite brand/shirt by texture. It's actually a wonderful experience.
Jen, if no one's mentioned this yet, try Clothes Mentor. It's a resale store chain (kind of like the grown-up version of Plato's Closet). So a lot of the clothing is clothing people never wore with the tags still on, or is lightly worn that they sold or traded in. I have a friend that swears by it.
Jen, bring an empty suitcase & go shopping in New York. I was just in Daffy's today, (where I have a store credit that I still haven't spent), and thought of you. No dearth of small sizes there; it's higher-end sportswear. Daffy's is kind of like Marshall's & TJ Maxx. The one that I went to is on Madison at 44th, which mean it's right near Grand Central Terminal. The first floor appears to be mostly men's stuff, with a smattering of home furnishings, but if you take the staircase down to the basement, you'll see the women's stuff. There's also a Daffy's on the West Side, on 57th Street. I got nothing today but nearly bought a pair of shoes regularly sold for $89 for $29.99.
Like you, I am now a size 2 or 4 petite for the most part. I hate to say this, but you might have to spend a little more for pants. For some reason, European styles in general are cut smaller. I did find some size 2 pants in Marshalls, I am surprised you didn't. And you really do need to try petite sizes whenever possible. However, I am shorter than you, so you might be able to get away with regular lenght. Sears actually has some decent petite clothing if you take some time and look through it all. Maybe you can find some things online. Just be sure you can return them easily. The home shopping channels have some decent clothes in petites and XS and returns are easy. Good luck!
I'm a size 2 and petite. Almost all of my clothes come from Express, especially pants and dress shirts. For other clothes, I'm able to jump around from TJ Maxx, Marshalls, Kohls, etc. for some knitwear shirts and dresses, but pants and clothes that should be more tailored are pretty difficult at those stores.
The Limited is great for suits, especially, and Banana Republic and Ann Taylor Loft have some nice things as well.
I'm a size 2 and petite. Almost all of my clothes come from Express, especially pants and dress shirts. For other clothes, I'm able to jump around from TJ Maxx, Marshalls, Kohls, etc. for some knitwear shirts and dresses, but pants and clothes that should be more tailored are pretty difficult at those stores.
The Limited is great for suits, especially, and Banana Republic and Ann Taylor Loft have some nice things as well.
I second Ann Taylor / Ann Taylor loft - plus at Loft they give discounts for teachers!!! (And at AT for students).
I buy quite a lot at Ann Taylor - it may seem expensive when you go in there but they seriously have a clearence sale every other week. I never buy anything full price, I either use my student discount or wait a week or two and get that same $70 cardigan for anywhere from 10-30 bucks.
Filene's Basement has a great assortment of suits all for around $100, and may sizes to choose from. Not sure if you need suits for teaching, but it's definately a great place to get mid range designers (Ann Klien, Calvin Klien, Tahari, Theory) at a great discount.
I also hit up outlet malls for Banana Republic, J Crew and Brooks Brothers, or shop mainly sales at their main stores. It seems Banana is ALWAYS having a sale (similar to Ann Taylor). Brooks Brothers only has then a few times a year.
Everyone here has great suggestions. I want to add re: AT and AT Loft: if you're responsible, get the credit card. It's the only store credit card I've ever signed up for. It scores you huge discounts, and they let you pay it off with your debit card at the kiosk right after the transaction. Also, never pay full price at AT or AT Loft - you should always be paying less than 60% or you need to go back later!
Coming to terms with shortie shopping is the first step. There have been many trips to major stores that have ended in tiny, tiny tears in my life because nothing fits. It took me a really long time to accept that it will be harder for me to find clothes that fit.
Try Old Navy! I can't wear the size 4s in most places. Sometimes Sears has some not too-teeny bopper styles in its Juniors department. Old Navy has size 2 and smaller in everything.
My problem is two-fold. I can't find the right size OR length. All the pants I find outside of Old Navy are too short.
I hear ya, sister! Small and LONG? Unheard of in the women's section. I shop where my daughter does - Abercrombie and Hollister - just because of the length.
But those two stores are costly! Old Navy is good, but sometimes their clothes are frumpy. JC Penny? Journey's? Eagle Outfitters?
So I have to try everything on at the moment. But combining online with in person shopping sounds like a great plan. 
