Have you asked her how she feels about it? Maybe she's fine with the pouch. Maybe she'd prefer her old plumbing back. I think I'd leave that decision up to her after she's informed about the pro's and con's of both sides.
The surgery itself should not take long. You'll need to tend the wound afterwards. Sometimes it's stapled, but mine was packed with gauze so it had to be changed daily until it healed up in about a month. Most times reversals are done shortly after ending chemo unless the patient is too weak.
Did your mom have radiation prior to her initial surgery? There are some trials now where they aren't using it at all, just chemo for tumor reduction prior to surgery. I didn't have radiation and consequently had an easier time adjusting after the reversal. The radiation causes a lot of collateral damage to the colon/rectum.
If your mom wants the reversal, I would stock plenty of Imodium, baby wipes, Colace (for constipation, in case things go the other way), Gax-X, and maybe panty liners or Depends for her first trips out shopping, etc. - just to make her feel more confident. Also buy a tube of Calmoseptine Ointment - it will help greatly with a red and raw bottom from going too much (it's called "clustering"), which happens a lot in the first few weeks.
As far as diet, start easy with low residue foods and gradually increase the types of food. Add new items every few weeks. If something doesn't work, then stop eating it and try again later. It took me a year to be able to eat popcorn. But I was able to eat fruit and salads after 6 weeks or so. Also, remember the same things work after the reversal that worked for the ileostomy -- bananas, rice, peanut butter, applesauce, oatmeal, starchy foods -- those are all good things to eat at the beginning because they lessen the odds of diarrhea.
Also, I can't emphasize enough the importance of probiotics. Her intestines have been "offline" for awhile now and she needs to repopulate her gut with healthy bacteria. That will help a lot with diarrhea and gas issues. Yogurt, kefir, or a probiotic pill will do the trick. I use Jarrow brand (Jarro-Dophilus + FOS). Try to get a brand that's kept refrigerated because they have the most viable strains of bacteria.
Hope this helps!
Stage IV, liver/lung mets 8/4/2010
Xelox+Avastin 8/18/10 to 10/21/11
LAR, liver resec, HAI pump 11/11
Double lung surgery + ileo reversal 2/12
Adjuvant Xeloda 3-9/12
VATS rt. lung 12/21/12 - benign granuloma!
NED 3/17/12 to 12/13/2017, CEA<1