Congrats on the new addtion, however rats are very social and you should really get her a same sex friend. They can get bored pretty quickly even if you are home all day. They really do need ratty company, and with a cage the size as hers another rat isn't going to be too much. Please do her a favor and find her another friend. If possible locate a responsible breeder in your area, or look into rescuing one from the shelter. The pet shop should be your last resort.