Both of them
It’s more likely to be due to her digestive system getting used to the iron content in the formula. It’s unlikely to be a milk allergy unless she was already reacting to your breast milk
Green poo is completely normal for babies on formula and watery is also fine. My LO only poops once a day and has been like that since she was born she’s now almost 5 months old and is thriving so I wouldnt be overly concerned plus it could take a while for babies tummy to get used to the complete change in milk x
Green poo could be milk allergy