Yes you can - in fact at one point she says 'I have 400 lb people who do this, and so can YOU!'
There are modified versions of most of the exercises (there are 2 ladies who do it with her one of them does the easier version.) What you do need to accept is that it is going to feel bloody hard. But thats kind of the point. If it doesn't feel hard it wont be changing your body...and it is only 20 minutes, so every time you think you just carry on, she switches to doing something else.
I really recommend it - just don't eat loads afterwards thinking you deserve it, or you will ruin all your good work.
Yes - it's pretty intensive for those 20 minutes though. Obviously you should be watching your food intake as well. As soon as you feel like you are not dying then you should move up to the next level or use heavier weights.