Personally, I'd go for a Nurse Anesthestist specialty if I were pursuing a BSRN. Yes, the liability insurance is high, but the net payout is still better, though the hours will obviously be unusual sometimes. I don't even know what a RN midwife makes. I do know that NP's don't really do much better than std RN's in most specialties. If she wants to have her own private practice (if legal in your state), then there's the business side of things to deal with. Med-surg RN's do a lot of grunt work but make good $$$ & there's no shortage of jobs. ICU/CCU is cush, but those depts are always struggling to survive on limited budgets, so the stability isn't there.
ER is good for learning the ropes & earning ones stripes, but the OTJ pressure seems to bring out the worst in everyone - including the ED/ER RN managers. The stress, politics, & bullsh!t typically rolls on the RN floor staff & burning them out. I've seen ED/ER RN staffing billets rotate personnel almost as fast as a carousel ride in an amusement park. Psych nursing? Don't even go there unless you love the specialty. Dangerous, & you have to associate w/ a fair number of substandard human beings...& then there's the patients. As well, there are also some incredible people working in those specialties. I wish the public had a better understanding about the nature of psychiatric conditions & treatment.
My wife was a psych charge RN for 14 years before she transferred over to the admissions/auth department, & she's never looked back. Her outlook probably improved ~200% because of it. OTOH, if your wife is willing to work (for less) in a small hospital, family practice, or clinic, it can be pretty nice.