Different things are going to help different people. What sounds like it will be "a break" from stress to you? I went to a T for a while who would tell me I should take a bubble bath. WTF? I wanted to work on my problems, not take bubble baths, so this was a no go for me. But to other people, a bubble bath might sound good. I felt stress recede when I worked on my problems and made progress. So not just sitting there but instead doing something was self-care for me. The other thing that really helped me was working very concertedly to get more sleep. A big battle, but it is worth it. My mind really wasn't working well without enough sleep. You will know the things that work for you...

I think the reason your T doesn't define self care for you is that it is not the same for everyone. If she tells you to take a bubble bath, and that is not something that helps you, then it is just a dumb suggestion and makes the client feel like the T is clueless. So to find what self care is, seek the direction of less stress.

Good luck.