Sounds like happy squeaking to me. Some rats laugh and chatter to one another (loud enough for humans to hear at least.) when they're playing or having a particularly good time. So unless the others are being rough with her when they groom, or your sleeve is very tight, I'd say that she's enjoying herself.
My 4 week olds are squeeking in their little hut, so I can't see what they are doing. Sometimes when I pick one of them up, they squeek, I'm very gentle with them so I know I'm not hurting them. Any ideas on why this is happening?
some ratties are just more vocal than others. One of my girls squeaks most of the time when she is being picked up but then she's fine, and she loves the attention.
In general squeaks can mean many different things. Think about your rat and what's happening at the time of the squeak, and it will become easier for you to understand your rats.
I have a funny example of the meaning of squeaks. All my ratties try to steal the others food, which is often followed by a small squeak of annoyance. I should squeak with annoyance when they try to pry my mouth open to steal MY food lol.