Ah, maybe she wanted to pay for it out of her own cash, as opposed to sponging off of Bruce, as that would implictly make Barbara less independant as a result.

Bruce has offered to cure Barbara in the past, for example Bruce had the Holy Grail and offered to use it on her (after testing it on himself to remove a bullet that was stuck in his leg in such a way that he couldn't get it out) but she turned him down.

I'll post the scene once I unpack my scanners.