It's a control thing at this point, time for her to "own" it. Back off, no reminders or nagging. Put the potty where it's most accessible to her and tell her it's her business to do her business, but along with that comes responsibility for her actions.
Get rid of the diapers and put her in cloth training pants. When she goes other than in the potty, she gets to clean herself and the mess up, whether it's in her pants or the floor. Always have her put the poop in the toilet and flush it, to reinforce that "poop goes in the toilet." Have her clean the mess (pee, poop or both) with paper towels and cleaner, (there's a natural antibacterial one by Method at Target and of course you can go over it yourself, but don't let her see you) and rinse and scrub her undies in the sink. There's a bar of pink soap called "Zote" that she can use for scrubbing. She puts the soiled laundry in the dirty clothes hamper. Then after that she gets to stand in the shower and wash herself off with soap. (Some parents recommend a "cool" shower to make them uncomfortable.)
The point is to make it time-consuming and not fun for her to miss out on activities she likes, (TV, playing, etc.) which will help her to learn that it's much easier to use the potty. I've also seen that some moms tell the child they have to do laundry before the child can put on clean undies and bottoms so she can't go right back to playing, another time-consuming way to teach the child it's easier to use the potty.
Also, find out what her "power" incentive is. Yes, you've used books, dvd's, charts and rewards, but you haven't found what works for HER. ALL kids are different so what works for your best friend's or sister's child won't necessarily work for her. Ask her what would help her to remember to use the potty, or take note of what she gets excited about, then buy it. The key to this is YOU own it, not her, she earns the privilege of using it for 30-60 minutes when she uses the potty on her own with no reminding. This way the incentive doesn't lose it's motivation like it does once a child owns the new possession, once they own it they figure, why use the potty? And you want to have it on hand, going to the store later doesn't give her the instant reward needed to make this work.
It may take a few cleaning sessions to get her on board, but it will happen, just be consistent. Hopefully she will be trained before the new baby arrives, but remember, potty regression is fairly typical when a new sibling arrives!