Etiquette rules actually dictate that family members do NOT throw showers. The reasoning behind this being that a host who is related to the guest of honor actually benefits from the gifts as well, therefore they are (in some twisted, unfathomable way) throwing a shower for themselves as well. This, like many rules of etiquette, is an out-dated concept that comes from a time when families were much more dependent upon each other and often had many generations living in the same household. The rule (I think, especially for baby showers) is rarely followed anymore.
That being said, you could appropriately argue that it would be improper for your mother to throw your shower.