I agree that your T is trying to help you, but it sounds like she is being klutzy at it. I suspect it would be more helpful for you if she said something like, "try to remind yourself" and "try to do grounding", and if she added something like, "you won't succeed every time right away, but if you keep trying, it will work more often and you will suffer less when the flashbacks happen," and maybe even, "try to notice any little bit that it helps, and that will help you learn this skill."

I have often had discouraging feelings and thoughts similar to yours when I've encountered "helpful" suggestions, whether in person or in reading. I eventually realized that I needed to modify the suggestions by adding the types of things I mentioned above. Another phrase that has helped me is to say to myself, "Every little bit helps," and picture little drips eventually filling a bucket. So I would suggest that you consider trying to add these (to me more realistic) additions to the suggestions. My suggestions might not be exactly the right ones for you, but the idea is to figure out what variation would be helpful for you (for example, the one Kiya suggested). And maybe it might help to ask the therapist to add them -- that they would help you persist rather than get discouraged. (But bear in mind that it may take her a while to learn to say them. But if you see she is trying, that can make a big difference. And if she has trouble learning, that can give her some accurate empathy for your difficulties, too.)

I hope this helps.