I can't stand the way my mom rubs her feet when she drinks coffee, is there something bigger wrong here?

Ask U physician. U should not hesitate when u see u physician to ask him or her any question u have , s/he likes to help u.
Rubbing feet. Depends. It doesn't sound to alarming if it doesn't bother your mother. Try ignoring it and see what happens. If she is not well then consult with your doctor.