I do agree it can be difficult and scary to tell someone you are struggling, especially mentally. But I do think it is an important step to take. Can you email a therapist in your area and ask some things about the process? It might be easier to email a stranger than to tell someone you are close to right now.

One way I like to bring up the topic of depression is to ask a question. For example, I would ask a friend: "Have you ever had depression?" Then no matter what their response is I would say: " Well I am experiencing it. "

I think having a guide in a way of how to bring it up might make it easier. Could you email your mom, and ask her how she is to start a conversation? Sorry I am all of the place.