Do I send ex-T a "gift"?

To start: I haven't read beyond the OP.

Don't send things like that. It's harrassment and can be seen as making a threat. You'll just get in to legal trouble.

And holding out for such a long time? That sorta shows vindictiveness on your side, and would be demonstrative of you refusing to try to move on. You sound like you are planning in advance to force yourself to hold on to this, how is that healthy? Yes she has caused a lot of harm. But any actions you take just for revenge and spite would be showing her that she made the right decision for herself.

The best revenge is to move on (yep it's hard) and have a happy and healthy life. If she then ever happens to come across you, she'll then see what a crappy T she was because you'll have made all this progress without her.

I wonder if it would be helpful in any way for you to perform some kind of symbolic act using some of the things you associate with the ex-T and contemplated sending her? For example, take some of those items and burn or otherwise destroy them in a safe way, in private? And then throw out the remains and try to reinforce a mindset of peaceful detachment, that these memories cannot hurt you in the future? Dunno, I have never had similar long-term resentments but knew some people who had found relief in symbolic burying.