The French Wikipedia says it's related to
Amand:
https://fr.wiktionary.org/wiki/Amantine
Like you, I can't find hard info on Amantine written with a "t", but it's very close to
Amandine, with a "d", and with such a little difference I find it quite hard to imagine as a completely different name with an etymology that has nothing to do with Latin "amandus" one way or the other.