1) ibs can be hereditary & this may affect your baby but moer so later than now.
2) my son was on solids at 3 weeks & my daughter at 10 weeks (if I recall rightly) & she was put on prune juice because of the severe constipation before she was put on solids.
3) in the old countries (europe etc) they used to give babies "solids" at about 2 weeks of age according to my local dr (female) whose grandmother was from europe & told her to stop being silly babies don't read books they just scream until they get the food (quantity & quality) that they need & till they get any problems fixed (nappy change, constipation etc!!)
you should check out some of the ibs sites for yourself & your baby, no point her going through more pain & trouble re health etc than necessary.