It's not yet revealed if she is the mother of Ameri.
Henri-kun falling in love with a human is one thing but having a child with a human is kinda off his morals. He is practically married to the Border Patrol.
Bet he let the girl go back to the human world with him leading to the exit and holding her hand.
And IF she is the mother of Ameri which will make Ameri a half human and half demon, the Summoning Day of the familiars would have been so WILD in school. Like what was she gonna summon?

Daaaaaaammnnn.
Henri-kun so eager to talk to Mama Iruma that he asked Sullivan to help him.
The yearning.
Bet they were each other's first love.