i believe you should listen to your mom, if you really want to watch an anime, prove to your mom thats there's nothing wrong with it....
there's a lot of anime out there with very ungodly stuff, many of which tend to potray christianity as some vampire fighting community, or the popular "fan service" of panties and stockings and what nots many of which are done out of ignorance from the creators part..... I have nothing against you watching it, but be careful of what you watch,
especially if you are young. your mom's only watching out for you, so just look out for the right anime ...