I want to get another rat but i dont know what to do?

hey i have a rat it is about 3-5 months old and i want to get another one i use to have two but one died form a reprstory problem. i hade my rat know buy itself for about 3 weeks to make sure its ok and i think she is. so i wnat to get another one to keep mine comapny but i dont know if mine will attack another rat. ok so my rat is 3-5 monthes old and a female so would she attack a new rat