Girlfriend’s sex drive decreasing

My girlfriend and I have been together for almost 2 years. As far as I know she has been taking lexapro since before we got together. At the beginning of our relationship our sex life was great, but slowly the frequency decreased. Now we rarely have sex and she recently pointed out that she has almost no interest in it. She says she thinks it’s her medication, and that her therapist thinks the same, but that doesn’t make a lot of sense to me as she was taking this medication well before we started dating. I need some outside opinions on this. Has anyone experienced anything similar? Is this a possibility? Any feedback is welcome