Student psychologists give high value therapy. They are supervised rigorously by upper level psychologists and professors. You do not have to worry about quality.
I have been in continous therapy for 26 years. It is highly beneficial for me. I have overcome many grave difficulties with the help of therapists. I have benefited enormously from their guidance.
I suggest you simply don’t think about how long you need to continue. Instead I believe it would be good to think about goals you want to work towards. You can ask the young psychologists to help you think of goals. My current goal is to be surrounded by kindness for myself, for others, and from others. That’s an example.
Keep seeing the students. They’re doing good work, and you provide a valuable service to them giving them real world experience.