Sorry, I can't help you here with any personal experience. With ex-T, I basically just blurted out at the end of session that I'd made an appointment with another T. I'd intended to come back for a termination session (or sessions), but never did. I talked to current T at one point about what clients tend to do in termination sessions, and he said how what I did, just announcing at the end that it would be the last session, is much more common than a formal "termination session." Or a client canceling an appointment and just never coming back.

I think I'd maybe want to talk over what progress I'd made, some of my successes, how far we'd come together. I'd likely tell him what he meant to me, though I'd be more likely to have written/typed that and handed it to him (or I'd be sobbing too much saying it). I'd probably also want to give him some sort of small gift, like maybe something I'd created (he's always tried to encourage my painting, so maybe something small that I'd painted)? I'd want a hug, even though my T doesn't give hugs (I'd hope perhaps he'd make an exception, but doubtful)--maybe just a longer handshake than usual (ugh, I miss in-person sessions so much...been virtual since March). Those could be examples of a more meaningful sort of session, wrapping up your relationship. Would she allow a selfie of the two of you?

Or might you want more of a fun, relaxed session? I know some posters have mentioned playing a board game with their T as a more relaxed session. Could you see doing something like that, where it's more of a fun session? Or, I don't know, make some sort of art together. Or ask her some things about herself, where she might be willing to share more than usual? Like, fun things (what her first kiss was like, how she met her partner, her favorite childhood memory).

You have a bit of time, so just try thinking about the sort of tone you might want. Also, is there a chance you could see her again after she returns from leave (if she plans to resume practice at some point)?