I'm sorry to hear about this, do you have some links to your GitHub and the interactions?
EDIT: I checked Leah's Mastodon, found this interaction: https://files.catbox.moe/6dftac.png
https://mas.to/@libreleah/111997718668105706
And here's the IRC interaction: https://av.vimuser.org/lorenzo.txt
https://libreboot.org/contrib.html#lorenzo-aloe
I haven't taken the time to read all of this fully, simply trying to share info that is not supplied by either parties.
EDIT: Taking more time to read it, it seems so far:
OP's code was buggy and bricking boards. Leah requested a patch to solve the known problems. OP took too long, and when Leah got a personal copy of the same computer/board, she worked on her patch and implemented it. OP is still listed on the site. https://libreboot.org/contrib.html#lorenzo-aloe
Provided hardware testing for the Dell OptiPlex 9020, also provided testing for proxmox with GPU passthrough on Dell Precision T1650, confirming near-native performance; with this, you can boot operating systems virtually natively, performance-wise, on a Libreboot system in cases where that OS is not natively supported.
All round good guy, an honest and loyal fan.
I personally have not written any code nor submitted anything to Libreboot, but it seems OP is still credited despite the claims of being stolen. I can't confirm if any code was used by OP or if Leah used 100% original code, as that's not my expertise. And even then, I'm not sure if the GPL/whatever license Libreboot uses is cool or uncool on that.