I agree with the empty stomach, biscuit at bedtime advice, but the runny bott is a bit of a worry.
It might just be a coincidence, and it could be the weather or anything snaffled on walks (Buddy has a different consistency every day - quite an art project really) but it could also be a sign of an obstruction. Although I would expect her to be unwell.
Just keep an eye on her and if she seems unwell, or if her tummy becomes rigid or sore then whisk her off to the vets. Otherwise, if she remains well in herself then just do the biscuit thing and I hope she will improve.
Sorry, not wanting to worry you, just want you to know what to look out for. It's probably not an obstruction. She would be pretty unwell if it is.
Hope she is better soon