I think it all depends on how vested you are in this friendship & in helping her & her daughter.
If you are 'done' with the relationship (and I certainly wouldn't blame you!) then yeah, call CPS... basically, let someone else (professionals) handle it so you don't have to continue feeling some kind of responsibility for this situation.
I really can relate to the mother in this situation (though I would never just drop my kid off & not come back)... so coming from that perspective, I would be heartbroken if you called CPS on me, and I think it would add extra stress to my life. What would be most helpful if it were me, would be a phone call, Hey my DH will watch your DD & mine, let's go get a coffee or something. And then lots of time to chat & try to see if you can pinpoint *her* problem, whether she's depressed or mentally ill or just really stressed. If you can, print out local resources for therapists, programs for SN, checklists for SPD, and things like that for her DD, as well as things for the mom like info on a mother's support group... However all that is a lot to ask of a friend (especially a friend who's already been lied to & taken advantage of), so if you don't have it in you to do that, don't! But that's what I think would help her -- having a break to chat, knowing a friend cared enough to print out all these resources, having someone help come up with a plan of action.....
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