I'm really really worried about my girlfriends health... help?

My girlfriend, she NEVER drinks water, ever. Instead, she tells me she ONLY drinks coke, and occasionally juice, milk, but NEVER water. She tells me she drinks coke everyday. Coke is really bad for the human body, it can dissolve nails, metals, etc. I can only imagine what it does to the human body ._. I mean I DO drink it, I gotta admit, but only maybe like, 2 or 3 times A WEEK. I drink lots of water. Coke is extremely bad. It also causes diabetes, and possibly kidney failure. I don't want my girlfriend to get diabetes, or kidney failure.. I read online that drinking WATER can dramatically reduce risk of cancer, while coke greatly increases it.. The LAST thing I would want is for her to get sick in any way... I try to convince my girlfriend to stop drinking coke and to drink more water, but as a result she generally gets angry at me for 'nagging' at her, and ignores what I say.. I love her alot. I do, I only bug her about it, telling her to stop drinking so much coke and to drink more water, 'cause I care alot about her and I love her alot. I don't wanna lose her. I don't even want to IMAGINE life without her :( Please help, guys? I hope she doesn't see this question ._. Anyways, lately, she has been telling me that she feels bad, that she has been having really bad stomach aches. I wonder if it's as a result of drinking so much coke and not receiving those nutrients and minerals found in water. I'm really worried because I had a friend once, that she was OBSESSED with drinking coke, and now she has a stomach ulcer from so much coke.. She has to take these pills to treat it, DAILY.. And she tells me it hurts, lots and that she regrets drinking so much coke. Now she won't drink it AT ALL. I hope my girlfriend doesn't have to go through that.. I'm so worried, I think about this every night :/ I dunno what to do :/ I really don't wanna lose my gf i care so much about her :/