DILEMMA!!

Yes, why not? If she likes you for who you are it should not be a problem, and even if she doesn't like it it's better to tell than having to hide it forever. http://www.theloop.ca/wp-content/uploads/2015/06/mansw.gif

Does she have any biases towards otaku culture? If so, let it in slowly. Otherwise, just have her sit down and watch some gateway animes with you, and when the subject comes up, spill the beans. You can't make someone else an otaku though. It either grips someone or it doesn't, and trying to force someone to like something you like is a violation of their free will to like whatever they happen to like.

Surely if you're in a relationship, you want the other person to know all of you, and vice versa? Whatever you do, don't pressure them into watching anime or reading manga if they don't want to - relationships tend to fail when one person tries to make another change.

i agree with ChocoBro. introduce he to your otakunice slowly, a little at a time, and see how she takes it. If she takes it well, let out some more. if she accepts pretty well, go all out weeaboo lol. Dont tell her straight up till you know for sure though.

gf:childhood friend her twin bro:my best buddy till now.. That is an advantage and Im going to use it..

maybe just lowkey suggest her a classic anime to watch, let her see what she thinks of it. If she enjoys it, then you can slowly introduce her to more general anime culture without going full blown otaku.