M.,
My babies also did seem to have gas early on, which I learned was actually colic. Sometimes it helped to place them on their tummies over my knees and pat their backs. This provides counter-pressure to the abdomen (as well as a new view of the room). You may also want to try a warm water bottle or warm bath to help relax her tummy and let the gas pass, if that is the issue.
I already see that you have many suggestions to try Gripe Water. It is a great natural alternative to the medicinal gas drops. I have been able to find it at my local Fry's grocery store as Gripe water is growing in popularity. It is usually with the teething gels on the baby aisle.
As for the feeding...you are not alone in struggling to provide enough breastmilk for your baby. Do not feel guilty. But before switching formulas again, consult your pediatrician. They might have more ideas for you on helping your daughter adjust to formula feeding. My sister-in-law also tried Dr. Brown's bottles (after Ventaire did not completely relieve the gas) and that helped her daughter be less gassy.