Shrubs are delectable! But they could be seen as an intimidating suggestion in this context. IKEA has some affordable fruit concentrates of lingonberry, blueberry, and elderflower you could substitute with a splash of vinegar for a refreshing lower effort treat.
Okay, so this isn’t actually about hydration, it’s about the fact that SSRIs commonly cause dry mouth as a side effect due to anticholinergic effects which reduce saliva release Some SSRIs are worse than others, and older TCAs are worse still. But OP is not dehydrated.
Water is great for hydration, but it is unfortunately not very effective at managing dry mouth due to these side effects. Flavoured beverages typically work better because they promote saliva release.
I would suggest OP add something with a sour note to their water, like lemon or lime juice which are unsweetened and have effectively no caloric component. Alternatively even just a splash of carbonated water will also work as the bubbles are irritants and will similarly stimulate saliva release.
For iPhones, if you have Find My turned on, you can’t activate the device without the iCloud password, unless the owner removes the device from their iCloud account. Which is what the scammers are trying to get her to do here.
The water moving right through is probably a good sign someone is well hydrated! There can be total body water versus intravascular volume depletion scenarios, but not super likely unless someone is sick in other ways.
The xylitol itself may be contributing to GI water losses (it’s only about 50% absorbed through the gut, and osmotically draws water into/keeps water from being absorbed from the intestinal lumen). Depending on the SSRI, this could be exacerbated by bowel irritability that can present as diarrhea (sertraline is notorious for this).
Some folks also report more urination with intake of sugar alcohols like xylitol. I don’t have a mechanism of action for that, so take those reports with a grain of salt. (And also some glucose because sodium-glucose symport allows for water absorption without the need for an ATP pump.)