I’m in need of some rat advice. I got two female rats (Wilma and Betty) last November, knowing rats are happiest with a friend. Around 4 months ago I had my sister rat sit for me as I was away for a week. When I returned, I came home to a lonesome Wilma. My sister had both girls out to play, as I had asked (I did say to only have them out if being supervised, but younger sisters r tend to not listen), but didn’t make sure the fox terrier was outside. Sadly my sweet little Betty didn’t stand a chance.
Wilma has been by herself for for the past 4 months, as I wasn’t sure if she would welcome another female rat. She is quite aggressive toward my while she’s in her cage, but fine with him when they’re both together out of the cage. I understand that there is a process to go through when introducing new rats and i’m 100% willing to do it the right way, but seeing how Wilma is to other animals while she’s in her cage worries me that she won’t accept new company. I don’t want any harm to come to her or the new addition.
Will it help if I get a brand new cage? Something bigger than she has now? She’s currently in a 1.5m high cage with 3 levels. All new bedding and toys?
Any advice will be of great help. I just want my little girl to never be lonely as I can’t play with her all day every day, as much as I’d love to

P.S The fox terrier is my mums dog and doesn’t live with me anymore, so there will be not threat for Wilma and her new companion.