I don't think she's necessarily depressed. Maybe she really doesn't know what to do, and she's too embarrassed or ashamed to admit that and ask for help. Frankly, I'm not surprised. There's so much judgement about mommyhood - how we should feel about our kids, how we should treat them, how they should act in society etc. Having a child with special needs probably makes it even harder to figure out the right things, especially with so much conflicting information out there.
Does her culture have more of a hands-off approach to parenting? That could be a factor as well.
As for what you should do, ask her if she wants help, and model good parenting skills that engage the children in a great way if you can. I think it'll be a hard conversation to have, without making it look like your rubbing it in her face that she doesn't meet your (society's/whatever) parenting expectations.
I have great empathy for this person.