I agree with ECE - it sounds like they are not coming back.

The fact that you said that she hasn't returned your call or even discussed the notice sounds like she is now uncomfortable to talk to you or doesn't want to do it.

I would half guess that the stomach bug is just a way to get out of bringing her to daycare and that the mom may just not feel comfortable in bringing her back. She may just be using the stomach bug as a polite non way of stalling/avoiding you and the awkward situation

How long is the notice period?