Guys need your help! Have some travel booked for rest of the year with my fiance. Trying to figure out a program to credit her flights.

1. She seldom flies alone, and I'm already an AA EXP. So status has no importance.
2. Most travel will be on AA, BA metal. About 40-50k Miles.
3. Leaning towards BA Avios due to household account = the ability to pool. I retain control essentially. But will she get more value out of AA miles?
4. She has some 300k in chase points, outside of that no ffp programs.

Thanks!