One big thing to consider is to make sure it truly is constipation. Constipation is when the poo is like pebbles - very hard and very dry and leave no mark on the nappy or bottom. Even FF babies rarely get 'true' constipation. The longer the stool is in the bowel, the more fluid is absorbed into the bowel, making them difficult to pass and in extreme cases it leads to constipation. And also just having made the switch from BF to FF can make the bowel need to re-adjust itself kwim? BF poos are very soft in consistency and FF ones are a lot firmer - quite often due to the higher iron content in formulas.

I think switching formula's will only do more harm than good ATM as she is only just getting used to the one you have and she will need to get used to a new one, possibly having the same issues. Give her more time, and try some alternative methods to help her - tummy massage and infants friend etc before making the switch.