You should take her to see a gastroenterologist, or at least get a second opinion. Bleeding with your stools is not a symptom of IBS and usually indicates something else like Crohn's, ulcerative colitis, etc. So does weight loss.
IBS is a diagnosis of exclusion: meaning that you must be tested to rule out all other identifiable physical causes such as Crohn's before you settle on an IBS diagnosis. Without having had a colonoscopy, endoscopy, blood tests, etc you cannot assume IBS.
I would start by demanding a colonoscopy. I don't suffer from Crohn's. I have had IBS for about 9 years now and have been through all the testing to rule out other causes for my symptoms. The first place the doctors started was with a colonoscopy. It's no walk in the park, but it will provide the best picture of what is going on in your mother's GI tract.
I will find a way or make one. –Phillip Sidney 1554-1586
All that I am and all that I shall ever be, I owe to my Angel Mother.
The Bucket List- Have you found joy in your life? Has your life brought joy to others?
Make sure your suffering has meaning…
As many as one in five American adults has irritable bowel syndrome. Most people with IBS find signs and symptoms improve as they learn to control the condition. Only a small percentage of people with irritable bowel syndrome have severe signs and symptoms.
Fortunately, unlike more serious intestinal diseases such as ulcerative colitis and Crohn's disease, irritable bowel syndrome doesn't cause inflammation or changes in bowel tissue or increase your risk of colorectal cancer. In many cases, you can control irritable bowel syndrome by managing your diet, lifestyle and stress.
I agree with Navy and Nanners..................your Mother needs a complete GI work up and you may find some great info in the Crohn's Forum.
Take care and hugs to your Mother.