When you say "let" do you mean a legit full time rental agreement, ie. she's gonna be living there as a tenant or do you mean she'll turn up for a few hours bung you some cash and get on with it. Yours is a grey area, if it was a totally separate building that you owned and you weren't around you'd probably be ok but as you are actually in the same building all be it she's in a self contained flat, you don't have as much plausible deniability, you probably will still be ok but it's a little too grey for my liking. Plus you just confessed to knowing to the whole world on here
LOL
** In the UK he could get done for living off immoral earnings as could any husband or BF living with a partner who escorts, although such prosecutions are very rare. **