How can a student stop/report conversations with a professor that make her uncomfortable, while avoiding negative consequences for the student?
This sounds like an instance of mental health problems on the part of the Professor A...

Probably it is simplest to behave "incomprehendingly", to just be unresponsive, disengaged, listless, and generally not react at all to the machinations of the person.

It is unfortunate, but does happen, than people (apart from gender issues) get caught up as "dupes" or "accomplices" in the schemes of mentally ill people who've managed (despite their problems) to get into situations where they have considerable power over others.

While in principle one can file grievances and/or hire lawyers (e.g., in the U.S.), this is often a path that has great costs, psychological, personal time, and one's reputation (even if one "wins").

So, as often is the case, again, if it is feasible, "playing dumb", being unreactive, and just letting the drama pass you by, is probably the most desirable/happiest approach.

(No, "justice" is not served ideally-well by this approach, but it may be served as well as can be...)