Awkward situation with Social Media

I don't usually have coworkers on Facebook but I couldn't resist adding my (attractive) PA. Problem is that she is very active on Facebook with many friends, including other coworkers who obviously know me. Every time I post something she "likes" it and I feel bad that I don't correspond. Why don't I? Because she posts pictures of herself sexy poses, in bikini etc . . .
I have to say I really do like her pics (wow) but if I click on that thumb button I'm going to be sending a wrong message aren't I? Better keep the relationship professional but hope she not offended