Raelle is not suppose to be Native American...
The cession is the land the American government gave back to Native Americans and each region is named after a tribe.
Raelle's family being descendants of colonizers lived in the area, when the govt decided to give land back to the Native Americans Raelle's family never left.
Also the actress who plays Raelle also grew up on Native land and both her parents are half or part Native.
As for the other stuff mentioned Eliot stated that the early ranks of Alder's were the enslaved African Americans, as someone said that would have helped abolished slavery earlier and I believe Eliot did confirm that slavery was abolished early..
And yes that does mean that Alder and her army fought the British and French and whoever else, as stated by Eliot, other countries copied what America did, so we don't know when but Alder and her army most likely only fought human enemies for a short time before she had to start fighting her own kind from other countries.
I also don't remember Alder's deal being that every female witch had to join the army, if I remember correctly it's every child born from a witch.