The way I see it, Tara isn't attracted to MC, but sees him both as a partner in crime, someone she can share her kink with, and as someone trustful enough that she can open fully to him, including physically. She knows he'll enjoy seeing her pictures, and she also knows he's not going to judge her for that, share them, or do anything else that would be problematic. It's a good way for her to open herself to sharing more, because she knows that even if the recipient enjoys it, she's still in good hands, and isn't risking anything.
It is, like other relationships, based on trust, and proofs of trust. She trusts him because he proved she can trust him, and that allows her to push her boundaries with him, and to ignore certain usual barriers.