I'm thinking of kicking my mom out since she can't afford the rent
Do you really feel like that warrants kicking her out?
There's no reason really to kick her out, I just want to get rid of her so I can relax
While it's your house and your rules, she is still your mother and it's only proper and kind to let her stay with you. You lived with her rent free for 18 years, so why not let her stay a few months without paying? People could assume you were being heartless for kicking her out.
Hey, I'm trying to solve problems here. If she can afford her own rent, then she can stay with us, but she doesn't want to.
I really feel like you should show some empathy in this situation and let her stay with you no matter what. I'm sure she's done a lot for you for free over the years.