It's understandable that you'd feel anxious telling your parents about your long distance relationship. I think it's great that you feel safe enough to open to your therapist about it. It's smart to share this information with your mother with your therapist there so she can help facilitate. Sometimes therapists have a way of taking what we want to get across and make it more understandable for the other party. By this time you would have already been in your session, but remember in situations like this that the best thing you can do is appear calm and confident. Your relationship makes you happy and it's good you feel you can open up to your mother about it. She may not understand it but it's you taking a step to nurture that relationship, which is important. If she is upset by it try not to react too strongly- remember she just has your well being in mind and she isn't your enemy- and try to find a way to work things that works for everybody. This can be a win-win situation and having your therapist there can help.
Please let us know how it went! Feel free to
PM me anytime. My inbox is always open.