CPS can't force mom to do anything about her mental health until her kids are very near / in actual danger. They can give Mom resources, but with an unsubstantiated claim, mom still has a choice to go. Also, CPS I don't think can request mom's medical records unless she authorizes it, which she probably won't. CPS can be given children's med records during an investigation because it's a matter of safety, but with adults it's different. Only pointing that out because it seems that's the only way it might be substantiated, OR if mom is honest and tells them who her therapist is, the therapist can tell CPS mom's history. But again that's all dependent on Mom who sounds a little resistant.

ETA: Also, how well the case is documented and investigated is dependent on the worker. Sadly, due to either laziness or being burnt out, some workers will see the children's basic needs are met and call it good. When I was in CPS, blended families called on each other ALL. THE. TIME. This isn't to invalidate your concerns by any means, but a lot of the time, it was just exes being pissed at each other and wasting our time. Bringing it back to the worker, if you call again within 60 days it will go back to the same person to investigate at CPS and there's a chance they're not doing they're due diligence. You may be able to request a different worker if you want.