should not wander off and leave me with her tres annoying 6yo while I wait for dd to come out of the shower at the swimming pool without asking if it is ok. 
Trying to MN in peace and said child will not stop talking, showing me stuff & demanding attention. Also keeps standing on tiptoe to see what is on my phone. Mum wandered off without a word nearly 10 minutes ago, as soon as the dd started talking to me and I wasn't rude enough to ignore her.
I know she might have had a long and tiring day, and perhaps she was just desperately in need of a break. I'm probably just being mean & grumpy, but I have had a long and tiring day too.
I wouldn't have minded if she had just asked if I could keep an eye on the dc for a moment...