Bitey rat

Can you give us a little more information? How long has she been doing this? Did something change around the time she started doing it? Do you pick her up differently to your mum? Do you use hand cream or lotions? Who feeds them and cleans them out? How old is your rat?

Based on what you already said, it sounds like you are going to have to go back to trust training, like you would with a new rat. Tempt her out with treats, sit and talk to her, pet her while she's in the cage etc... baby steps. Once she starts to trust you reasonably well, you could consider forced socialisation, though not everyone agrees with this method. You could also consider having your mum break contact with her for a while, so that she has to come to you for treats or food or playtime. It's hard to say without a little more detail.

So was Loco with you before Beckoned moved back in, or did Beckoned bring her with her?

It sounds like Loco is more tolerant of you because you're the one that looks after her... Beckoned just wants to pick her up and fuss her and she's a squirmy girl that doesn't care for that too much.

Are you a little more sure in your handling, perhaps? Rats can sense if you are anxious or nervous, so it may be that she nips you less because you are more confident with her?

Perhaps you could switch positions for a while and have Beckoned be the only one that feeds and handles her... see if that encourages her to be a bit nicer? Other than that, the only idea I have is to start again with her as a new rat and build up her trust... rewards for good behaviour, possibly forced socialisation etc.

It sounds like she's territorial over your mum, then... and possibly the cage. Your mum mentions she's nipped her a couple of times - was this when she was getting her out of the cage?

OK, does anyone have any advice on dealing with territorial rats, please?

I haven't had to deal with this before and my book doesn't say much about it, but I would suggest trying to entice him out of the cage with treats. Make him want to come out to you, instead of grabbing him. Hopefully, others will have an idea what else you can try for this.

I'm sorry to hear you didn't manage to resolve this problem