don't give up.
She is very little and her latching might improve later on. My second twin was impossible to latch and didn't breastfeed properly for six weeks; suddenly when he was quite ill he got the hang of it - possibly wasn't struggling so much and just relaxed and took what was on offer vecause he was thirsty
I mixed fed for about four months due to these difficulties (although had planned to exclusively bf) and then when they were weaned into solids (admittedly in those days earlier than now) I was basically breastfeeding both of them with not bottles of milk at all, and also they had dairy in form of food, rice pudding etc, cauliflower cheese, drinks of juice and water. Went on for 2 years, happily breastfeeding.
I breastfed the first baby whenever I could (complicated by her needing top ups for low birth weight) and just formula fed second baby, with a bit of expressing thrown in, and sometimes expressed milk in bottles. Then I moved onto giving them both the breast by six weeks with bottles of formula at times of day when cluster feeding made life very difficult, ie 6pm. I religiously ebf at night because I found this was quite a good way of stimulating supply and also more convenient. But as I say second baby only had bottles until he was six weeks as he literally wouldn't take any milk from breast at all (possible tongue tie or tongue thrusting)
Just feed the first baby from the breast as much as you can, perhaps have some formula for the second one and then keep trying him on the breast and DEMAND Feed as much as possibly rather than getting tied up in expressing routines.
I felt it was better to keep breastfeeding by this method than to feel like I had failed because I wasn't exclusively breastfeeding and then give up earlier.
lack of sleep makes breastfeeding so exhausting but formula fed twins can be just as exhausting in other ways. There is no quick fix, and I felt by four months breastfeeding did make my life a lot easier.