Arching back is a sign she's having pain in the tummy. Can you try giving her gentle a tummy massage when that happens? You can do bicycle legs also.
Yes, please upsize to 3m+ And if baby doesn’t throw up or regurgitate milk, you can try without the burping during the feed:)
If she drinks less per feed, would you like to try adding 1-2 more feeds during the day time to see if the total volume can increase? At this age, my LO was also very resistant to drinking, and needed frequent breaks in between feeds, so she had many small feeds. The Ridwind helped her to pass out the gas more easily and be less fussy. Post vaccination fussiness lasted up to 10 days for my LO, especially the rotavirus vaccine, which made her tummy very uncomfortable.
Donutella