Unless your Mac was left unlocked and unsecured, there was nothing installed.Why do you say that? There are legit keyloggers that people can purchase to monitor, say, their childrens’ web habits. It’s not entirely far fetched that this person could have installed one on my iMac. I’m just not sure if she would have needed my password to do so.
Yes. If you are running a few recent OS, they wouldn't have been able to install such to begin with without Gatekeeper and other triggers flagging it. I think you are worried over nothing.It was unlocked. But to install software such as a keylogger, would they have needed admin privileges?