Yeah, I know poeple like that. They give with one hand and take from the other. The result is the recipient feels like turning down the money would be far less trouble than taking it. Oh, but, then you get the guilt trip along the lines of "our money isn't good enough for you."
You're venting here, and that's good.
Here is my suggestion, speaking as the mother of adult children.
Suck it up.
Just take her money, listen to her bitch, then go on your merry way. Very soon, you will be self-supporting and won't have to go through that crap just to get money promised to you.
Then, later, when you have children make a vow that you will give them money with with very well defined strings attached, but no more.
All money comes with strings attached, without exception. The trick is you don't want to pile on more strings after the money has been accepted.
"OK, My Child, I will give you $5,000 towards buying a car, provided it's American made." (or automatic transmission or post-2005 or whatever)
"Mom, I really appreciate that. Thank you."
You buy a Ford, thus fulfilling the condition on which the money was given.
"Can't you take off work and give Grandma a ride to the shopping mall? After all, we did give you money to buy a car."
That's adding a string, post-facto. You can get angry, vent, etc., but the correct response is:
"I'm afraid I cannot do that. I have to work. I'll call Grandma and see if she's willing to go some other time when I don't have to work. I think Grandma and I can come to an agreement."
I've mentioned on this forum the difference between Private Thoughts and Public Expression. Sure, in your private thoughts you are seething angry, and rightly so, just like the message you wrote. Keep all that in your private thoughts. Your Public Expression should be "I am so grateful to Mom and Dad for helping me with my education. It was a lot of sacrifice for them."