Make sure she has access to a litter box when she is out.
Also, if you don't have at least 2 rats, you need to have at least 2 same sex rats (there are established, gradual intro steps for introing rats if any are 12 weeks of age or older- so that no one is hurt) as rats are social and need to live with at least one friend
Covering furniture with large fleece blankets will help to protect it.
I cover carpet with large pieces of thick linoleum.
Rats will teach themselves to use litter boxes most of the time but they will scent mark .... and walls behind the cage will also become yellow so a sheet of chloroplast behind the cage is a good idea.
The way to "teach" your rats to use the litter box is to put a litter box everywhere they like to go .... lol ... corners and the bottom of ladders are popular places.
most of us wear "rat clothes" when our ratties are out - clothes we do not mind being peed on or chewed.
Also, it is viewed as a compliment if your rat pees on you as you are being urine marked as theirs.