M.,
It sounds like your sister is a wonderful mother. Tell her to keep up the good work, and the breast feeding will get easier for both of them.
Some things to consider/try with regards to what looks like an obvious reaction to the formula and/or mommy's diet (colic is almost always linked to allergy or stomach issues caused by allergies).
Gripe water for the tummy aches. Works wonders!!
Probiotics for the tummy will help eliminate the need for zantac (which is dangerous for babies and can lead to issues later in life). Look for something that contains at least Bifidobacterium infantis. I can get you a list of products if you'd like.
Also, I would most certainly suggest that she change formulas. Soy isn't always a better option, but she can try looking at the two formulas offered here <http://www.naturesone.com/products.php>. The formulas are listed as Toddler, but are complete for infant nutrition (I have spoke directly with the company on this topic). These are the two BEST options available commercially.
It would be best to keep the baby on breast milk, of course and there's a great resource available she can look into for that. It's called MilkShare and it's a way for mothers who want to provide the best for their babies but can't for WHATEVER reason to do just that. Here's the website <http://milkshare.birthingforlife.com/>
Finally, if your sister consumes a large amount of dairy in her diet, have her cut it out completely. See a post of mine for a wonderful list of better non dairy options for calcium <http://www.mamasource.com/request/recent/17356/1171977501...;
Blessings for your sister and her new little one. And for you to care enough to ask.
Rolinda
Wife, Mother, Friend