Why do some married girls have the need/desire to fix up their single friends? Is this rude?

Talk to her. If she does not get the hint,and you don't want to hurt her feelings, then pretend you are seeing someone say you are going to the movies etc... It is not lying because going out with yourself and spending time with yourself is better than going out with a guy sometimes. It does not mean she is unhappy maybe she just does not want you to be alone. Good luck sweetie