My son had severe reflux and was on Prevacid also. We used the Dr Browns wide bottles and the Playtex Drop Ins. The drop ins work really well because you push all the air out of the bottle so there is not air for the baby to ingest.
I HATE the Avent bottles! They leak unless you have the lids on them just right, not too loose and not too tight. They are very touchy!
Are you using formula? If so, are you using the powder and shaking it to mix each bottle? If you are, that could be part of the problem. If you are using powder formula, mix the bottle about 10 mins before the baby wants to eat because this will allow time for the bubble to settle.
Also, there are many options available for formula, including some that are for gassy babies and some that are for reflux babies. Ask your pediatrician if they have any samples of other formulas you could try. Just keep in mind it takes about a week on a formula for a baby's system to adjust and to determine if its the right choide for her.
Mylicon drops are safe to use with every feeding. Burping more often, keeping the baby upright and still during a feeding and for about 30 mins after a feeding can also help. My son spent a lot of time in the bouncy seat, swing and propped up in the boppy to help with his reflux and gas.
When she is especially gassy, moving her legs in the motions of riding a bike can help to get the gas moving in her system and help her to pass the gas to become more comfortable.