Sheep will commonly scour when their guts aren't used to fresh grass, if it's a slightly greenish scour from grass colour, and she is otherwise drinking, eating her creep/hay etc and bright and happy, then it is likely from that.
If she is off colour, not eating, drinking as normal, check things like temperature, gum colour and perhaps consult your vet, but at the moment, it sounds quite likely to be 'nutritional scour' from fresh grass.
Hope that helps
Suzanne