Is there a god of magical girls?
There are...gods who can
apply to magical girls? And some who would happily claim them as part of their domains/conceptual realms/general idea. Some magical girls definitely do their thing as an aspect of their existing faith, or who utilize powers granted to them by a god as part of their toolset. But the idea of a singular "unified purpose, only I get to be the god of magical girls" god? Nope.
To try and make this clearer, with some random examples: Let's say you have Urgot, who is a god that was formed by a small community after they were forced to leave their home to help defend them on their long journey until they wound up in Orion City. He protects the lost, refugees, and fugitives, offering shelter and safe guidance. He would probably say that Magical Girls are guides to the lost, that they are fugitives from the law, and thus would easily fall under his domain if they so choose.
At the same time, Salaria, a goddess formed by a group of 'already mages' who wanted to engineer a god that would help them to push for, say, magocracy, and thus embodies a conceptual idea of 'right to power coming from magic', would obviously say that they're part of her general remit as well - They easily fall under the idea of the right to power coming from magical strength and the enforcement of justice springing thereof.
Both of these are theoretically "gods of magical girls". But the concept of a magical girl is still really loose - There's no real unifying ideology, community, or theme beyond mild aesthetics and general intent to "do good", which isn't exactly enough to create a god. Plus, they're still relatively new - It takes a few years of belief and building up their power before a god can do much! If they persist as a societal trend rather than fading out, you might see a few gods formed by communities of magical girls, who get together for that purpose, similar to gods who are formed by the Guard or other organizations, but at the moment, no, there is not a specific agreed-upon "god of magical girls".