When I made this phone call I was at the other end of Canberra! So Katy and I raced home, bundled Pippa into the car and drove to the vet. The vet looked at Pippa's paw - and explained that he didn't think it was a grass seed because the sore spot wasn't in the web but rather at the base of the toenail. He suggested that they keep Pippa for the arvo and put her to sleep to inspect the paw properly.
After picking up Ella and Andy, we headed back to the vet to retrieve Pippa. The vet had discovered a cut near her toenail and a very wobbly toenail (although not wobbly enough to come out). Obviously this had been causing Pippa a little bit of grief. While Pippa was under, the vet decided to check her other paws and low and behold she had a grass seed in each of her back paws!
A groggy Pippa was happy to head home with some antibiotic tablets and cream and the damage ($$) for us wasn't too bad either :)