It sounds to me like the other parents/maids might be as much to blame. If they're deliberately missing your daughter out when giving out treats etc, then the kids will be picking up on this. I suggest you take the bull by the horns and approach the carers directly - they'll probably be shamed by your direct action and realise that they have, in effect, been guilty of bullying a small child.
I get quite worried when I hear about people having problems like this when they move to Singapore, as I have not yet moved there, but will be in the next few months and I've got 2 kids - so I hope the kids in the condo we're moving to aren't too clicky.
Good luck and I hope your little girl finds some friends soon.