Kids (or rather adults, since that's what they are when they go to college) should pay for their own college, even if it means borrowing the money. College is an investment, and funding your own investments (whether using borrowed money or not) motivates you to (a) choose good ones and (b) put in the work to make it pay off.
Now how many presents has she bought for you? How many presents have you bought for her?
Is there some "quid pro quo" you can work out? I recently spent $200 on my own purposes, with another $200 to be paid within the next three months if all goes well, and by pairing it with the purchase of things she's been wanting for a while, I think I made a nice quid pro quo that made everyone (including me) happy.
Having her hold whatever she's been paying for over your head indefinitely means that you'll never be in a position to buy anything at all for yourself. Not a good position to be in. Whatever she's contributing to your kids ought to be revisited, both for their own long-term good and for the purpose of getting you out of her debt in both your minds. This is absolutely crucial for your happiness, for her happiness, for her respect for you, and for your respect for yourself.
a fine and enviable madness, this delusion that all questions have answers, and nothing is beyond the reach of a strong left arm.
