Definitely get her to see a doctor! Ring the out of hours emergency doctor line (usually on voicemail on GP surgery telephone number) at least, if severe (vomiting, pain...) I'd go to A&E.
For how long and has she got abdominal pain or other symptoms or other medical conditions? When did she last go to the loo? Could be some kind of obstruction and not something you want to mess about with. I'm not medically trained though and don't wait for an answer here - ring and ask a doctor and let us know how you get on. They will be able to advise best.