Combined with symptoms of weight loss I would be concerned about the rectal bleeding and glad to hear she is seeing a specialist soon.
IBS is usually a collection os symptoms affecting the bowel and from what I understand (from having working in colorectal surgical area) NOT inflammatory in nature and not likely to cause rectal bleeding.
All rectal bleeding should be investigated regardless of whether she has haemorrhoids or anal fissurs in the past. I hope for her sake its not crohns disease!

Hope she gets a clear diagnosis and is feeling well soon. I don't envy you having to get her to her appts either so big hugs to you as well.