I responded to your last post and this clarifies what I said in that response--as you are finding out, it may be POSSIBLE to potty train a 17 mth old but it's not going to be EASY. Several people said they trained their young child, so I'm definitely not saying it can't be done, but believe me it will be more work for you than if you wait. Exactly what you are experiencing! My 2 yo seemed trained and then started having accidents again. The only thing that worked was giving her a tic tac every time she made it to the potty--but again, at 17 mo they are much less able to control their bodies and understand about the reward, so I don't know if it will work then.
One thing the doctor told me is not to "waffle," in other words, once you decide she's ready dont' put a diaper on her again ever. Don't keep going back and forth. It will be messy!
If I were you I'd just wait!
Blessings,
Lynn