If it is a joint account, then both of you have equal access and both can see the activity in the account. If you changed the password, that won’t help since you probably get mailed statements (and anyway, your mother would sooner or later get her password fixed, and might also suspect you changed it).

So the only solution is to open your own account, preferably at a different bank.

You are unable to do so i’m sorry I have done research for ya and it is not possible you could change your online banking password thats about the only way she could not see it. GOOD LUCK