An ailing resident in a ritzy Upper East Side co-op building stabbed her home health aide in the gut during an argument over her oxygen mask, sources said. Kevin C. Downs for NY PostThe victim was rushed by ambulance to Weill Cornell hospital, where she was listed in stable condition. 3 The fight in the ritzy pad was allegedly sparked over an oxygen mask. Kevin C. Downs for NY Post3 The victim was rushed to Weill Cornell hospital, where she was listed in stable condition. Kevin C. Downs for NY Post“I had just come back from running my errands and was having a cigarette and she asked me for one,” he explained.