baby with gastro issues

My six month old grand-daughter weaned herself from breast feeding at four months, is on similac sensititve formula for lactose-intolerant babies, "spits up" a lot and often, doesn't swallow baby cereal/food well, and only has a bowel movement every 3-4 days (thick, heavy, dark). My daughter's pediatrician doesn't see any problem - just says every baby is different. She doesn't have colic or cry with gastro issue so no one is concerned. I am because our whole family has a history of GERD and IBS. I would really like to know if something can be done for this little angel early to help her avoid the problems many of the rest of us have had. Any guidance or suggestions would be greatly appreciated.