force grooming

Question
So I have two female rats and they are both around one.  They were not raised together, and I got them both separately.  My one female, Lyla, was by herself for about 8 months before I got the second female, Geri.  I know it's really bad to leave a rat in solitary, but it took me a really long time to convince my boyfriend to get another one.  

Geri, I adopted/rescued from a psychology lab experiment.  She was in the "control" group, so she was never tested on or anything and she was raised with several other females.

I really don't know much about Lyla.  We got her from a pet store.  She's always been a bit hyper and she chews on her bars and she's just a little nervous.  She's a really sweet rat though, and she loves to be around me and my boyfriend.  

The thing that is really bothering me about Lyla though is, she forcibly grooms Geri for literally hours at a time.  They really are great friends and I know they like each other's company, but it's upsetting to see bald spots on Geri where Lyla has just groomed the hair off of her.  I don't know what to do about the situation.  I would be upset to get rid of either, and I know neither of them should be kept alone because rats are social, and plus I can't afford another cage.  Are there any good suggestions to get this to stop besides separation?

Answer
To be honest with you? I tell people this: There are one or two things you can try and if it doesnt help, the best thing to do is not worry about it. Really, it sounds like a cop out but its the only real solution if nothing else works.

Two reasons rats power groom each other or themselves:

1. Dominance
2. Boredom

Do you have enough toys and things in the cage for them to play with?  How long do they come out for playtime daily and what does their play time consist of?  Curious as all heck by nature, rats want to explore and if it is the same old thing day in and day out, boredom sets in. A fine example are my baby boy rats. I made a huge play area for them using 4 foot tall cardboard sheets all taped together to form a big square and it goes around their cage. I put in some toys like a few boxes  etc...and at first that was fine, they had fun coming out to play and they were so tiny they were safe and secure in the play pen. I sat in there with them. Within a week they were bored so they started to climb the cage. I quickly changed their toy selection and started to do this every few days and they quit trying to find ways to leap over the cardboard!
I always tell people that have power groomers (another word is barbering)to keep them busy as much as they can, letting them out to play and keeping them occupied during playtime. This often gets results when it comes to barbering.

The second choice would be simple dominance. Some rats just feel the need to prove themselves to the other rat.  Her attitude may be "Hey, I want to groom you, so I will, like it or not!"

Usually though, its kind of psychological either way when it comes to power grooming so we have to try different things to see if there is a response.

To be honest, I only see power groomers change "sometimes" and it usually is when the rat simply grows out of it. Otherwise, there is no real way to stop it except to try to see if stimulating their little minds will help.

As long as the other rat is not screaming her little rattie lungs out and there is no real fights over it, she may not even mind it much.  I wouldnt mind someone giving me a back rub every time I sit down to rest.  LOL