My baby has a rash on her stomach and is teething. Is this normal?

Possibley. Teething would not cause a rash on your child's stomach. The rash is most likely the result of something else. But babies getting rashes and teething are all normal parts of growing up.
Likely not related. Teething will cause some some children to become more irritable and uncomfortable. You will likely also see an increase in saliva flow and the desire to chew on things (like their toys). It should not cause any rash however. The two are likely unrelated. I can't comment on the rash as it is out of my scope, but i can say with confidence they are not likely related. Best of luck to the little one!
Multiple causes. The rash could be due to several causes and one would need more details to diagnose it. Teething usually does not cause a rash. It could be due to a viral infection, allergic reaction, irritation etc. Please see you pediatrician to get it diagnosed. Hope that helps!