Well now your going to have to find a way to fix the girls cage so she cant get out and now that she can get into the boys cage, your going to have to find out how to fix their cage so this cant happen again. Find out how she got in, ect ect.
You can also check if she has a plug, rodents leave a white like substance that hardens so no other male rats can breed with the female they have bred with. I'm sure you'll understand where that plug will be. :|
I don't think theres any real concern for panic here rats are not ALWAYS in heat, so she could have just been curious... Anyway, as was mentioned you definately need to escape proof your cages and you should probably consider spaying your female, it reduces the chances of benign mammary tumors, and that way you could put her with the males, though i'm not sure if intact males would fight over her? I know guinea pigs do.
They were fighting. I am not worried about it to much though. She doesn't seem to be pregnant if she is we will find the babies good homes. She only got out because one of my little sisters accidentally left her cage open and shes sooo tiny she can slip through the bars on the boys cage. She can not get out of her cage though unless its left open. I will make sure they don't open the cage anymore without supervision. I don't think it had been long because I had just fed her. Thank for the advice though! I will let you all know what happens. We had baby rats once before and it was a lot of fun and they all got good homes! I'm not scared at all.
Female rats go into heat every 4 days, so there's a pretty good chance. Even if the "visit" was short, rats can mate in mere seconds.
You can weigh her daily, you can get her e-spayed, or you could, I guess, cross your fingers and hope for the best. I don't recommend that!
Of course, if you do think she's pregnant and will allow the pregnancy to continue, I'd suggest making sure you have enough cages to separate the babies at5 weeks and start seeing if there's an interest in babies in your area.
Though you've been through this before? I guess you already know that.