Doesn't necessarily mean she looked you up. I have had many people show up as friends suggestions who I have never considered looking for. On occasion, it is a student or former student, or some odd acquaintance or distant relation that I have no interest in interacting with. No idea why some of them showed up - it's that weird six degrees of separation thing I'm guessing. I've been known to proactively block those names so it stays a non-issue.

Seems entirely ethical to block clients if it is the therapist's policy not to interact on social media with clients.