it should be okay for awhile but i wouldn't keep her in it for too long,if you can't get baby rats i would get adults and breed them your self,but you could wait till she is about 3 ft or so,and for size i've heard that snakes grow about a foot a year,and for size i'm not sure how you get your snake to grow as large as you want it to be but i would figure a good home regular feeding and good care and she will grow,hope she does good.