hi read your query will try to respond as simply as possible see she feels thirsty cause she has diabetes, and has possibly high sugars that need further control. So drinking diet coke will not help- it will only raise the sugars. she may have water for thirst. besides she has water retention, and she is taking diuretic tablets, so again she is bound to feel thirsty. again drinking coke will just be counterproductive. coke has fluid too after all. she also has high blood pressure, and though not significantly proven that diet coke increases bp, excess sugar intake she has from diet coke will definitely raise her sugars thereby affecting her bp so i would strongly recommend against diet coke. if she has to drink, let it be water. i hope that answers your query please feel free to ask further queries Dr Saumya Mittal (if found helpful, please mention so)