Why has my rat changed?

Question
My boyfriend and i have two 3 month old, female, dumbo rats. We bought them from a pet shop which has a good reputation.
When we bought them, we were informed that the smaller one of the two, Foofoo had had mycoplasmosis, but obviously had recovered sufficiently enough to be sold. She is about a week older that the other one, Gutso, however is extremely small in comparison(Gutso, hence the name, eats alot and is a good size). They have both been really friendly, cuddly and very active since we got them, and we love them to bits! However Foofoo was out with Gutso playing and then she suddenly just dashed under cover and completely changed. She became very nervous and seemed to just want to be on her own and didn't want either of us near her. She was very sleepy and just really didn't seem herself. Normally she is cheeky and will do little tricks. We left her cuddled up in a blanket for a while and then put them both back in the cage.
Foofoo immediately ran to a level at the top of the cage and remained there for most of the evening. We moved her after a few hours and found that she had urinated, and remained sitting in it. This is obviously unusual as rats are clean animals.
We went to see the vet the following day and she did not know what was wrong with her, and gave us some anti-inflammatory and antibiotics. No sooner had we got her home though, had she brightened up! The vet had suggested mixing the drops of medicine into a bit of jam, and giving it to her, and we did this as soon as we got home. Also she told us to add apple & blackcurrent squash to their water to encourage her to drink, so we also did this. We don't know whether she seemed better because of the sugar, or whether she was just pleased to be home! The next day i was watching the rats and Foofoo's behaviour was still very strange. She is still not herself. Then i noticed that Gutso was pushing little Foofoo around. She was grabbing her ear and pulling her about. Foofoo would squeek but would not run away. This went on for about a day or so, and i intervened when i heard her squeaking and stopped Gutso from doing this to her. We researched this kind of behaviour on the internet, and were also told by the vet that their hormones are starting to kick in, and so thought that as Gutso is larger than Foofoo, she was trying to be more dominant than her. The following day, Foofoo's behaviour was still not normal but i noticed that she was starting to stick up for herself! Well..i think that she is, it could in fact be that she has given in. She was partially climbing on Gutso's back and either cleaning her or nibbling her back. It was difficult to establish whether she was biting her or not, but Gutso was squeaking. Foofoo's behaviour is still not normal, and it is worrying me that there could be an underlying problem with her health or whether she is just not feeling herself because Gutso is trying to gain dominance. The vet briefly mentioned that rats get Meningitis and i am worried in case she has that, or something seriously wrong with her! Im really attached to them, and am desperate for someones opinion! Do you think that it is behavioural/hormonal, or do you think that it is to do with her health? Thank you for any advise that you can give me, Eleanor.

Answer
From what you described, FooFoo panics and runs to top level of cage, this is a clear sign of respiratory distress. Rats that have a hard time breathing will panic and seem anxious and often seek the highest level of the cage to try to compensate for lack of oxygen. They also tend to hang their head over the edge of a shelf or if they are on top of a toy house etc..they extend their necks over the side.  The medication may have helped but if she indeed has myco, you need to read up on myco on my website.  In order to prevent chronic lung disease from chronic myco, they need treated properly.  This includes being on the right medication that is specifically for an organism that lacks a cell wall, like myco does.  Baytril and zithromax along with doxycycline as a back up are the drugs to use in this case and should be treated for no less than 30 days with newest studies saying up to 6 weeks.  I studied myco extensively as part of my training in rat health care.  If this is not done, she will have another relapse and this is when lung damage occurs.  Scarring and blistering is common usually on the third myco flare up.  
Please read up on it here:

http://www.freewebs.com/crittercity/mycoplasmosispage.htm

Also, meningitis.  Yes rats CAN get it but its not half as common as you may think. I am sorry the vet scared you. I have had a handful of rats have it, only one survived it and he is blind now in both eyes.  He had it in January and he is now just turning 2 years old. We did blood work to find out what he had and this is how we found out.  His brother had it but passed away.  Its not common though even though I have had rats have it.  I have had over 40 plus rats so 4 out of 40 rats isnt so bad. Mammary tumors in female rats are more to worry about than meningitis is.
You should think seriously about spaying both girls to prevent the growth of these tumors.  Read about it here:

http://www.freewebs.com/crittercity/allabouttumors.htm

Anyhow, I think it could be a bit of both, although the girls are not yet nearing puberty. Their hormones will not start to change till they are closer to 6 months old and menopause hits between 18 months and 2 years old.  They are sexually mature but they are not socially mature, so its not really a hormone issue.  

Hopefully she is being treated with the right medications and she will continue to improve.   

Is your vet a certified exotics vet or just a vet that sees exotics on the side along with dogs and cats?