Be careful about labeling someone a covert narcissist as it can get you into constantly looking for that in your mother when she may be just a nosey mother. It's ok to set your boundaries when it comes to sharing your finances with not only your mother but others, it's not something I care to do either and a lot of people dont.

It could be that she just doesn't feel comfortable with showing her emotions with people, some people prefer to keep their feelings about things to themselves. You have a right to set boundaries with her and if you think she is trying to get information from you in round about ways, then just stay on firm ground with your boundaries and change the subject. Now you know to avoid even telling her that your rent was raised.