Hello Joshua,
I was working as an architectural designer on a construction project. It wasn't an architectural practice but it was design and construction.
You can do this while working for a practice. You don't need to take time off just to put this together. In fact part 3 you must be working while studying.
I won't be able to comment on your gf's position. She must contact RIBA, ARB, and course providers.

Thanks,
Aditya