I'd looked there, it's not spelled out. Maybe I'm mis-remembering?
I don't recall Lara
ever spelling that out in a plain-talk manner, something that was unambiguously a suggestion/offer.
She has spent her whole life (a couple of centuries
at minimum) working the flirt-and-tempt angle. Even if she meant it seriously, I think she'd couch it in flirt-and-tempt ways (and, consequently, Harry would always see it as a predator's lure).