Perhaps she does think you will have challenges along the road and isn't sure how you will face them. And she doesn't quite want to say that as she perceives it might be discouraging. One approach would be for you to work hard on your most difficult issues now--anxiety, depression, low self esteem, or whatever they may be--then come back to this question after 6 months (or sooner or later) of working hard inside and outside of therapy to overcome what is your greatest challenge to success in school right now. Ask her again after you've made concerted progress and see what she says. If you know your professors were wrong about your performance in the class you failed, you now have a chance to prove them wrong. If you think your T was swayed by reading your profs' report, then take the class again, and show T your passing grade. She probably doesn't need it, but I think it may be important for you to be able to show her it.

Work hard on your issues, make progress, and do well in the class. This would be pretty convincing!

Maybe it's not so black and white. Maybe the answer is something like, "if you work really hard on your anxiety (or whatever), and work hard in your classes, then I think you can do this." I think, in the end, what is most important is how you answer the question yourself. We should be the ones who know ourselves best. If you know you can do it, then I believe you can.