Hi are her stools watery? NOt to be confused with loose stools, watery stools and increased frequency could be diarrhoea.
Has she had anything else to consume other than FM?
Eg. Touch things then put in her mouth/put things in her mouth, or the bottles and equipment havent been cleaned and properly sterilised?
If she seems Ok, still active and not cranky, then you can observe the stools.. if she is listless and "off color" better bring to pediatrician.
For my 3 mths old, he used to poo several times a day, then reduced to 1x a day when he was 2+mths .. Now, he poos once every few days (3-4 days)..
But he didnt strain to pass motion, not constipated, still happy and active, feeding well on TBM, when he eventually passes motion his stools are soft not hard, so I just let him be.