Sometimes I think some parents volunteer at a school just so they can lurk around school, take liberties, and make everyone feel too awkward to sit them down for a serious conversation about boundaries.
One thing I've learned while teaching: There's love, and then there's obsession. And I admit that I say that without having an understanding of what it feels like to be a parent. But I remember by upbringing. Mom and Dad made mistakes, but they never made me feel like this flawless being in need of constant attention and protection from everything. I remember mom holding me and saying, "I wish I could take the pain away, but this is just part of growing up. It hurts, but it will pass." How many times must she have wanted to march into my school or badmouth another parent. But she didn't. She didn't gossip about other people or assume that I was 100% blameless. I am lucky enough to know mostly amazing mothers who love fiercely while still understanding that some things children say must be taken with a grain of salt, AND that hardship is necessary for growth. And if this particular hardship which has me so aggravated were putting this child in serious emotional or physical danger, of course we would intervene. But it just isn't, and she won't accept that.
Get another volunteer opportunity, lady, because we don't want you. Get your own life.