It’s normal at this stage, she will get better with time. My breastfed baby has the same issue so the formula is not the problem.
My baby did the same, up until about 13 weeks he was only pooping every 4-5 days and when he went he was straining, crying and struggling. When he would actually go it was completely normal. A lengthy google search found Dyschezia and basically, after their newborn reflexes don’t make them go they have to learn to do it themselves. Mines 17 weeks now and poops daily
This is common with new babies. They’re essentially learning how to poop, as long as the consistency is normal they should be fine. They’re not constipated and I wouldn’t want to change milk just yet. If poop stays normal I’d just let her work it out herself. It’s hard but if she’s just learning to poop she’s not actually in pain she’s just straining all the muscles!