Breast fed babies can pass pasty stools.
Since you say its watery and 7 times, I guess she is having a gut infection- mostly viral. Usually its seen associated with fever
Continue to breastfeed. Its better to avoid the powder milk you are giving.
In viral diarrhea- only thing you should take care is prevention of dehydration
Be sure he drinks enough breast milk. You may also give her Pediatric ORS
Usually formula milk will not be tolerated well in kids with diarrhea .In such a case you may try giving her soya milk which will be better tolerated.
She must wet her diapers at least 4 to 5 times a day. If its less, it means she is getting dehydrated.
Though she is only 3 months old- you may try giving her yoghurt- which has probiotics naturally.
You may also give her probiotic sachet like Econorm- about 1/3 rd sachet twice a day.
If its viral, she will be okay in 3 to 5 days.
At any time if she develops high grade fever, she is dull, urinary frequency is very less, she passes blood in stools- please do not hesitate to visit your Pediatrician
Hope my answer helps you.
Wish your kid a speedy recovery.