I’m sure your sister is probably going to be quite annoyed but. . .you are correct and she is not.
Canon law requires that for a period of one hour before reception of the Eucharist one must not ingest anything other than **water or medications. **The relevant passage from the Canon is below.
Canon law states, “One who is to receive the most Holy Eucharist is to abstain from any food or drink, with the exception only of water and medicine, for at least the period of one hour before Holy Communion” (CIC 919 §1)
Now I personally love tea of all kinds. . .but I would not drink it within the one hour prior to receiving the Eucharist. (That goes for coffee too, for all the ‘coffee hounds.’)
Your sister needs to switch to water only if she must hydrate herself. Does she also drink iced tea throughout every **other hour **of the day, I wonder?
She also calls you a ‘nut’? Hmm, I think she has some other things she needs to address in confession along with unintentionally breaking the fast. (Now that she knows what she did was not right I’m sure she’ll want to acknowledge this.)