Then I'd strongly encourage you to block this person and cease all contact.... Even without photo's being exchanged, you could still be done for grooming a minor.
It doesn't matter what "she" says.
As a matter of law, you have no protection, and no defence.
None.
Seriously, drop this thing.
Before the cops come through your door at dawn.
I think you are leaving yourself open to all sorts of problems and that you would be better off finding another outlet for this kind of thing. The optics of a man in his 40s wanting to engage in sex chat and exchanging of pics with a 17 year old are terrible.