Been through something so very similar with my dd, who is now 14 and in yr9, but in yr 7 she was the one always pushed out of the group.
She hadnt told a lie, but she is a lovely girl, who was a bit naive, and suffered hugely at the hands of some really nasty girls.
One of them was supposed to be her best freind, but eventually,.after meeting with the head of year, and encouraging my dd, she moved on from this, got other freinds, and is alot happier now,
She only has a small group of freinds, and is by now means in the "popular" gang, but she's not like that anyway and is happy.
IF the head of year is not forthcoming I would go and sit in the schools reception until such time she will see you.
I agree that sometimes we shouldn't interefere, BUT this is year 7, 11 year olds, they are still children and deserve our protection....many girls this age mature (!) faster and can cope with these situations, and evn thrive on causing them.but alot of girls are not mentally prepared for this, which I think shows in the fact she lied in the way she did, and she needs you to do whatever it takes to help her.
I don't think you should be flamed for her lie, we bring our kids up to be true and good but FGS, they all tell little porkies, and she did this to try to be more interesting, it was not a lie meant to cause harm!
Does she have any freinds out of school? encourage her to find some after school clubs she would be iteresetd in, and she can make new freinds maybe that way.
I wish you lots of luck, its bloody hard to think someone wants to hurt our babies, but support her, be there for her,and encourage her to meet some new freinds.
x