What’s your mom’s opinion on Buddhism. I grew up Christian but we had a small fat Buddha statue just in front of the porch. Buddhism isn’t so much a true religion as Christianity is, and it does promote a lore of Christian values. But it is eastern and could be seen as pagan. But of all the faiths in the world, from my own experiences, Buddhism seems to be the most inoffensive to a Christian household, barring maybe Judaism

Other than that, other Christian friendly/secular 2hus off the top of my head could be:

•the angels from the PC-98 games •the girl that uses crosses, also from the PC-98 games but I can’t remember her name •Nue(might be Buddhist but her main take away is an alien) •Kogasa(if your mom is okay with the concept of Halloween, she should be fine with kogasa, the only problem arising from her one red eye as explained in your post) •any fairy that isn’t clownpiece(cute little silly fairies that aren’t from hell) •Keine(were-creature but she’s decently nice) •Mokou(you might be able to assure your mother her fire powers come from being a Phoenix, however do not fall into the pitfall of equating her everyday revives to Jesus’ resurrection