Given that she is the Mother of both the Ulitimate "Good" and "Evil" I always pictured her as Neutral.
She doesn't show that much concern for Humans or lesser races.
She is pretty much like a mother watching her 2 sons fight and getting badly injured, though she seems to favor the "Good" Son for his benelovement nature.
She'd probably be happiest if her Sons make up, even at the cost of all living beings on earth.
If you switch from the good path and get your alignment to evil by the time the dream with her near the end of Act I happens, she specifically says that "her side" is "the path of light"; that doesn't sound like neutral to me. And you yourself say she favors the good son because of his benevolent nature, a
good attribute. Benevolence isn't neutral; if one were neutral they would tend either to something more like minding their own business or even apathy. If she were neutral, why would she favor someone for their good attribute?
There is something to be said about trying to keep a balance and being neutral in that way, but if that were true, she wouldn't say that being good is "on my side" when talking to the MC in the dream. "My side" wouldn't be good, but you only get that conversation if she's trying to get you to return to good. And, of course, this is underscored by the fact that she won't appear to you unless you've started on the good path. Yes, she can still appear if you've started doing evil, but it's based on the
good path. (One can even see this in the code, if one were to look.)
Yes, it's true that she loved both the Dark God and the Light God, "as any mother would love her children", but loving them doesn't mean she's neutral or that she won't take actions to thwart her evil son. If a loving parent who does good deeds (charity, is kind to others, etc.) has a child who becomes a murderer or rapist, they can still love the child. That doesn't mean they're OK with their child doing evil things, nor do they lack an opinion on what their child does or try to find a balance between their own good acts and the evils their kid does. TBH I don't think your logic tracks.