I'm a "veteran" of the 30DS and love it. I like Jillian and find that she motivates me. I started doing the program at around 190 or so, and I'm a little shorter than you, if that helps to know. Here is some advice:
- Absolutely do NOT feel bad for taking a rest day once or twice a week!!!! Take it! To go from being sedentary to doing 30 days of exercise that is that intense is a recipe for burnout and injury - neither of which will help you with your fitness goals.
- Modify the movements (even jumping jacks), even when Jillian tells you not to.

Jillian is not in your body, YOU are. Only you know when you're pushing yourself too hard, or not hard enough, or just right. Again, injuries and burnout and fatigue will not help you at all.
Remember, Jillian is saying a lot of these things because she's trying to motivate you to keep going and work hard, and that's good! But if you allow what she says to have the opposite effect - of feeling like a "failure" or thinking you can't do something so you might as well give up - then you need to consider not listening to her.
For the record, I stayed on Level 1 for over a month (doing it 4-5x/week) before moving on to Level 2. Then I progressed up to Level 3, then eventually started rotating them (at that point I introduced other DVDs, too, because it was getting a little boring - I also started muting the TV and putting on fun workout music to listen to, since I could quote Jillian as she was speaking

).
I don't think of myself as a failure or quitter because I took longer than 30 days. Giving my body rest days - yes! you need them! - and not allowing myself to become mentally discouraged was really key in wanting to keep going.
You can do this!

Just don't be down on yourself for being wise about doing it right, in a sustainable way.