Hi S.,
The Costco-version of Enfamil probably had a lot of iron in it. That is typically what constipates babies. Look for an Enfamil formula that doesn't have iron in it, or doesn't have as much.
How old is she? If she's started solid foods already you could also add prunes or spinach to her diet to loosen her BMs.
For immediate relief of gas, try laying her on her back, grab her feet, and move her knees up to her chest, then straighten her legs, over and over until she passes gas. You can try both legs together and then if you get nothing, one leg at a time kind of like bicycling. If she's too upset to let you move her legs, pick her up, hold her facing away from you with one arm under both of her arms, and grab her bum and rotate it in a clockwise circle, like hula hooping. Both of these poses help to pas gas that is past the point of burping. (See the book Itsy-Bitsy Yoga -- great book!)
You should also consider the bottle you're using, I know they have special "no-gas" designs now.
Good Luck!
:) G.