ASPCA | Cat Litter
the only thing i can think of that would be sand like is cat litter
make sure they xray her to make sure no blockage as cat litter has clumping stuff in some of them and if dogs are running free as well as cats then possibly a litter box she could have got into
I would ask groomer about that asap
some litter box train dogs too not just cats so either the treat or this - will try to think of anything else