My advice is grow up & stop being a self centered princess.
Your mother is a kind compassionate woman who wants to make her son's GF feel welcome. Your mom is treating this woman like a member of the family. You are treating her like an intruder who is taking away from you. You'd do better by embracing the fact that you have a new "sister" & learning to be kinder to others.
If you think GF needs to be a better cook, help her to learn to cook. If you want a particular dish at a family dinner, make it.
Seriously the world doesn't revolve around you. As soon as you get that message & stop being annoyed, you will be happier. Right now you are raging because you fear this woman is taking your place. That is the true heart of your problem & jealousy. Her existence is your new reality.