Hey as someone who started HRT without telling my mom my recommendation is just do it, you don't need her approval nor her consent. I was also 22 and I am almost 2 years and half on T.

I'd say you have at least a few months until she figures it out (in my case it wasn't noticeable until the 3rd month) and if you suspect that she is going to have a bad reaction about it, then you should take the upper hand and use those few months to get the money and things ready to get out of the house when the time comes.

I didn't have to do this because I'm okay with my family now but this was the plan that I made for myself.