Sorry, I wrote a long reply and it appears not to have posted successfully. I'll try again.
Would it be better to change her nappy before feeding her then to avoid this ?
Possibly so, give it a go - can't hurt

WRT infacol, its great at making little bubbles of gas into bigger bubbles - great for making burping more efficient but if the air doesn't come up, it can hurt a lot more further down. Perhaps try not using it for a couple of feeds...
When she's fed, you can put her on her tummy with her legs curled up under her - that can help, though you must watch her, can't leave her unattended if she falls asleep like that.
Burping techniques - try circular rubbing on her back rather than tapping/patting. Also worth trying burping her lying on your arm so you've got some gentle pressure on her tummy. When she's squirmy and upset with gas further down, you can do tummy massage (rainbow shaped movement with your fingers from her right hip, up across the bottom of her ribs and down to her left hip) and pushing her legs up into her tummy to help move the gas out.
she had been given gaviscon from the dr but it made her constipated so I stopped it, not sure if it made much of a difference anyway.
Was this for reflux? If so, perhaps another trip to the doctor for another option would be an idea.