"Oh, cousin Jeremy had to work all the way through college? Poor guy. I am so lucky that I don't have to do that this time around."
"Wow, Mom. I thought you would be happy for me. I'm sorry that my good fortune is a problem for you."
"Mom, why are you making an issue of this? We aren't struggling and we aren't asking you for any money. We are really happy about this so I don't understand why you can't just be happy for me."
"Wow, Mom. I wasn't looking for your approval; I was just telling you what's going on in my life. Why do you think it's okay to judge a decision that DH and I made? We are happy and it doesn't affect you."
Whatever you do, don't jade. It doesn't matter what your reasons are. Put it back on her. Why would her initial reaction be negative, instead of excited for you? Actually, you could ask her that very question.
"I was just sharing my good news with you. DH and I are excited and happy about it. Why is your immediate reaction so negative? That's really disappointing; I thought you would be happy that I am doing something that I want."