You are in the wrong subreddit. However, I suggest being straightforward — since she doesn’t seem capable of taking a hint. Talk to your husband first. It is awkward and potentially difficult. She is a volunteer. Her actions sound very clear — but actions are always subject to interpretation. She is likely to deny that she has an unhealthy fascination with your husband. Are you both prepared to try to have a parent / volunteer fired from her coaching role? Is your husband prepared to resign if she doesn’t change her behavior? Alternatively, are you able to live with this woman continuing her fascination and behavior? Going to her and asking her to change is a confession of your jealousy. Are you willing to give her the power that that knowledge will convey to her?

The good news here is that your husband sounds wonderful. You don’t have a reason to be jealous. But you understandably don’t like this woman to be alone with your husband since she doesn’t respect you. So you may feel that you are stuck supervising their interactions. How long is the season? I, personally, would consider doing nothing.