Your mother has an unreasonable (as in, she cannot be reasoned with) position on this issue so any attempt to reason with her is doomed.

Also, arguing with her at all is tacitly agreeing that she has a say over your bodily autonomy, which she might arguably have when you were a child but which ends the second you turn 18, if not significantly before.

So, don't tell her anything. Just stop wearing it and have her disown you, or however she's going to react. She isn't reasonable about this issue, so there's no point trying to be reasonable back.

Like - do as much research on Islamic scholars as you like and try and find the arguments against wearing a hijab - I'm pretty certain the original muslims didn't have to, it was a later requirement and was a culturally Arab thing that's spread everywhere, not an original muslim requirement. Though I could be wrong - but is your mother going to be willing to listen to all these ancient imams? Nope, she'll just consider them apostate (or whatever the term is) and ignore them.

Similarly, you don't have an argument as to how not wearing a hijab somehow proves your great (or greater) devotion to god, so, realistically, you don't possess an argument that can sway your mother.

So arguing is useless - so don't argue. Just do what you want and face the consequences.

What is your mother's opinion of / how does she view / what does she say about your father's relatives who don't wear one? That's likely to be a toned down version of her opinion of you if you decide to stop wearing it.

My only practical advice is that your mother will view this as a rejection or her and her values, and you should make sure she knows that it's not a rejection or her, just of her values.