Much of what you describe sounds bad, and reflects poorly upon your parents and especially your mother, in particular the very strange act of texting the coach WTF? But for the sake of a complete perspective I’ll offer you the most charitable defence I can of why she’s acting this way.

One lens through which these years of discouraging behaviour is that early in as you say, you came in with a lot of excitement and confidence that perhaps may have been premature at the time and maybe at the time she was concerned that you were setting yourself up for a fall and in a fairly misguided way was trying to protect you by trying to pull you back a little and keep expectations realistic so if the reality didn’t reach giddying heights you wouldn’t be devastated. If that is why she’s been acting this way, it seems she went all in on this notion and didn’t realise it was doing a lot more harm than good. I think that this probably then accidentally have became a sticking point between the two of you and she lost sight of her original intention and became more focussed on “bursting you’re bubble” and began to take all evidence that there wasn’t really any such bubble and that indeed you really did have realistic ambitions as a need to be even more critical than ever and so the goalposts have moved and moved.

This interpretation doesn’t exactly make her look saintly either but without knowing too much about her outside of your story it’s at least plausible and at least started with arguably good intentions. I’m not saying necessarily this is definitely what’s happening but you’ll probably have plenty of responses already covering how bad this looks so an extra perspective might be helpful to you. Up to you with you proximity to it to assess how realistic this could be.