In a very real way you stand between your wife and your daughter. She is very vulnerable to indoctrination from any source, let alone her own mother. That doesn't mean you should attempt to indoctrinate her first; that's just as bad. It simply means that you need to be the voice of skepticism in any conversations about Ba'hai, or any other belief. It sounds like nobody else will be.
Of course you can't be there every moment. However if your wife privately tells your daughter things about the faith that would not convince you, firstly she's picking the easier target and secondly she knows on some level that her reasons are not sound, and is using them to preach anyway. Both are dishonest, and she needs to realise that. Her first act as an evangelist should be to convert you, not your daughter.
Pay attention to your daughter, that's the main thing. If you think she's not thinking about something the right way, it's your job to put her straight. That's just one of the things you do generally as a father; this is no different.
Though you have every reason to be concerned, don't worry too much. What probably started me on the road to doubt was the simple fact that my father, someone I respected and looked up to, did not buy into religious belief like everyone else (it seemed). He only bothered to tell me he was an atheist about once. Your mere presence as an unbeliever may well influence your daughter greatly.