Thanks for all the info guys, seems the only sure way is a secret source of income that you get in cash.
Like gambling, crap solution though, and not very dependable.
I also use the work expenses trick, though I tend to spend that money punting whilst on the business trip, must work on improving my self-control!
The girl in question is well known to the forum, the reason for the possible change in spending habits is something I asked of her, so no need to worry on my behalf, though thanks for the concern which is genuinely appreciated.
Not going to tell the tale for reasons you'd all (mostly) agree with if you knew.