The fact that she has IBS does not mean she can't get sick from something else. The way you describe the pain is "textbook" for appendicitis
. However she needs to be examined by a physician for better recommendations. However appendicitis doesn't last for 2 weeks!
If the pain is severe, and she is having vomiting
I agree that you are better off taking her to the ER, particularly if this has never happened before as bad as now. She may also be suffering from a viral gastroenteritis
associated with cramps, indigestion