I think you need to elicit from her exactly what he said that offended her so much. There may be so much more to this than you have been told, and perhaps it might alter your own thinking about the wisdom of his being your rebbie. She needs to be utterly candid with you.
Just as an aside, sometimes women have a better intuition about certain things than do men. We read body language, we interpret signals differently, and even Avraham Avinu was told by Hashem to listen to all that his wife said, regarding Yishmael and Hagar. This young lady could be noticing things that you as a man, have not. Or, this could all be conjecture and she may be overreacting to something completely innocent.
In either case, you absolutely MUST have a candid talk with the young lady, and find out what’s bothering her. Communication is THE most important thing in a developing relationship, and if she cannot be honest with you about her concerns now, then she will not find it easier in the future.
After you talk to her, then I think you need to speak with the rabbi, and get his perspective. He may be unaware of something he said or did that bothered her. Or he may not have done or said ANYTHING that should have bothered her. Find out.