For me it has been tough. I do not have any loose skin after 110lbs loss (give your body time to adjust, especially if you are young) but the belly has been the last to go. It's probably because I am a guy and we carry our weight there. So an extra 5 or 10lbs makes a real difference to that area. As a lady you may have more luck. But you probably won't get an arse or thighs like mine either.
The rest of me is cut.
My guess is you have to get your body fat pretty low to have well-defined abs. For just a flat stomach, not so much.
And loose skin is anyone's guess but if you are young and your genes are so inclined etc. etc. you probably will be OK.
Exercise, especially strength training, really helps with loose skin by the way. Not just in the abs area but everywhere.