@Georgia sorry I should have added this all in. I am feeding her upright & she is 6 weeks x
What bottles do you use? It might be the bottle, some teets are different shapes, have you tried different bottles, maybe give a different one a try and see if she takes that better? My first drank way too fast, she was on extra slow flow teets because she did the same thing where she was inhaling it and ended up throwing it all up. My first was on tommie teepee and my 6 week old is on mam ones as she wouldn't take to tommie teepee ones. The mam ones are more of a flat teet which she seems to like better. I'd maybe try a different bottle with the no1 teet and see how she takes that xx
I think it’s better for go up a size in teat rather than use vari flow. My eldest never liked them, he spluttered all the time. Maybe try size 2 x
How are you feeding her? Is she laid down? My health visitor with my first showed me how to feed her sat up, it makes their flow to their pace rather than them laid down and just it going straight down. Maybe try that? How old is she also? It might be that she might need a different teet x