I have a wonderful rat named Daisy. She's just about as sweet as can be. I take her out for hours of the day and she seems content, as she bruxes and boggles very often. I do feel guilty, though, as when I am away, she is left alone in her cage. I'm thinking of getting her a friend. The thing is, I've had Daisy for 8-9 months and she's gotten very used to being alone. I'm afraid that if I did end up buying another rat, she would be defensive/aggressive towards the other rat. What should I do?