Is money received from my mother every month an income?
I will simply repeat what I've said in the comments, just so that there's a concentrated version of the argument.

What you are describing is not 'income' but a kind of 'transfer' payment. Your mother transfers an amount of money from her account to yours.

It is possible to consider it an 'investment' on her part; she would be investing in the increase of your human capital stock; such an approach would imply that she would have a claim on a part of your future income stream.

Since, usually, parents don't enter into contractual agreements with their children concerning their future income possibilities (that I know of) I would argue that from the viewpoint of you both, what you are receiving and what she is delivering is a cash transfer.