I would never take a dog any where with out the owners permission. The beach is a fun and very dangerous place to take a pet. They don't know that they should not drink the salt water. This has cause death in some cases. If you don't keep them on a leash, they could easily become over powered by the waves and dragged out to sea. In the hot summer time the sand is not only very hot on the paws but very abrasive, acting like sand paper. I think you are very lucky that fun was had by all. I would be very apologetic about the wounded paw. And assure the owner that you will never take her beloved pet anywhere without her approval.