A four-year-old Euless girl drowned in a Bedford swimming pool yesterday.  Alyze Martinez was pronounced dead at a Bedford hospital about an hour after she was pulled from a swimming pool behind a home on Chaparral Court near Pipeline and Brown Trail.  Police say the mother is a caretaker for the homeowner and took two of her children to work with her yesterday.  When the mother and another child went inside, Alyze fell into the pool.  As paramedics arrived, the mother and a neighbor were doing CPR but it was too late to save the little girl.