We do not decide who we are attracted to. Inital Attraction is a hormonal response to another based on a variety of things. I agree with much already stated that you are an adult and fully entitled to make your own decisions re: personal relationships. Many parents have a,hard time accepting our choice of romantic partners for many reasons. Some (like your mother's) are purely based on their own opinions and stigmas.. Hopefully, when you do introduce them to someone,you are serious about, they will be able to eventually accept your partner. Parents may think they have an ideal for their children's lives.. They have been dreaming of all the good things they want for you since before you were born, so it can be hard for them to change that image when confronted with a different picture...but truthfully, at the end of the day, most parents just want to know that their children are happy, healthy, and secure.
So overtime if She can see that whomever you choose to spend your life with treats you right, loves and respects you, and that you are happy...I hope she will eventually come around ....until then, you do not need to tell her the specific of who you are dating or if you are even dating at all.