i go to pilates and love it! There are loads of DVDs online (sorry, not used any though) but i have used lots of exercises demonstrated on you tube! They're fab. TBH if she tries one or two pilates classes to learn the basics she could then just do at home - thats what i do - i go once per week but actually spend 25 mins per day at home - once you know the moves you may aswell do it on your own when you have free time. There are some basic principles about how to hold your body in position but its the same for most moves so once you've learnt that theres tons of info on the net showing exercises you can do.
I would say you need to go to a few classes first to ensure you are getting the 'core' right. A good instructor will have a small class so they can get around to each person and ensure they doing it right and adapt exercises to their 'flexibility'. Otherwise pilates isn't very effective.
Once she's knows how it feels ( you can tell when you've have got it right) then get some DVD's. I think I might look at the library too..... You can get resistance bands pretty cheap in sports shops and the internet.