I understand why day care Mom upset too.

She come to you with issue and likely felt that not being heard but instead her son being blamed for not telling you! I know you not mean that way but it does seem a bit like you saying "well what you expect - I can't deal with things I not know about" rather than just apologizing and asking for some time to take in this new information and absorb it and come up with method to address. You took personally because it your kid, and can understand if client felt you hit back at her child.

I admire day care provider who has own children in business because must be hard to totally remove parent hat and deal totally with all children equally. For me, it not situation I had to deal with but would be easy to be too hard on own kids to avoid accusations of bias or too easy going cutting them slack because home no longer sanctioned family place.

Why you think your daughter behave like this? Is she resent her Mommy not being exclusive to her? Is she annoyed that her home/toys/life is shared with other children who not family, who she not like? Must be hard to have persons she not like in her home. As adult, I not ever have to put up with people I not like in my home so must be really hard for small child.

How long you had day care? Is this always been her life, maybe she getting fed up with it? Or is this fairly new and maybe novelty of lot of children now worn off?

These not really questions to answer just something to think about. I believe your daughter mis-behaving is her objecting to something she not like so maybe if you able to figure out what she's annoyed about, can tweak that situation (or ride it out until phase passes) but would be powerful information for you to have.

If she really fed up with other kids, can then take steps to give her escape once in while, carve out some time to dedicate to her weekend or evening, but something to reassure her that you still just her Mommy and the other kids are just work.