My admittedly sensitive 10 year old girl is one of only 7 girls in her class. One girl has a bit of a pick on her.
She regularly puts my DD down, e.g. negative remarks about new school shoes/coat/schoolbag. She'll whisper a "secret" in the other girls' ears and ask them not to tell my DD. If another girl or boy is chatting to DD in the playground this girl will intercept and pull them away. DD got a watch for her birthday from her sister. The girl said to all the girls in class that she'd seen it half price in the sale over the weekend (not that it matters, but it wasn't, and DD was hurt).
This girl is the self-proclaimed best at dancing, singing etc., the most beautiful she absolutely isn't, not that it matters , reckons all the boys fancy her because she's the most mature and has started getting boobs and pubes 
. My DD has a couple of boys in the class who are friends but not at the fancying stage yet, unless you count Niall from The Wandies.
This morning she burst into tears saying she didn't want to go to school because Gemma was so nasty. She has other friends in the class and in other classes in her year so I hugged my DD and told her to stick with them and ignore Gemma who must be a bit of an idiot (my words to DD) if that is how she behaves.
How do I handle this. I only had to speak to school 2 weeks ago about another girl who was taking the piss of DD because of where her dad is from 
saying she hated people from there. School handled it well and immediately, I must say.
This is low level but ongoing since September. I know Gemma's mum but not very well. I wondered if I should just phone her and how to start the conversation or just speak to the school again? It is parents' evening next week. My other thought was to make a point of saying "hello, how are you, Gemma" with a big smile and mad staring eyes in the morning in the playground. I don't normally go to the line in the mornings but thought maybe my presence will support my DD and maybe let Gemma know I'm on to her, without saying anything.
I'm glad I'm not 10 any more, it is a rotten age for little girls and friendships.