NTA at all! As a fellow long haired gal, I hate when people say this to me!

But also, you can fight this with facts. Look up locks of love and other companies requirements. They typically require a fill 12" to donate when your hair is pulled together in a ponytail which means even more than 12" of your hair gets cut off. That would probably force you to get a pixey cut in order to donate, not just a short hair cut. Plus, at least one of the bigger named donation charities doesn't even accept hair donations anymore. Synthetic hair has gotten so much better over the years and is so much easier than real hair donations, and so many real hair donations have been provided over the years, that donation charities don't even ask for hair anymore, they ask for money to buy and make synthetic wigs. Look all this up and show your mom and shut her up. You're definitely not TA.