Check out the FlaskScarf for women; they come in a variety of colors and stripes and have a hidden bladder than can hold up to 8-ounces of booze (or whatever). When you're thirsty just suck on your scarf!
From the makers the FlaskTie for men:
If your mom isn't a scarf person, there's always the classic tampon flask (which comes in a set of five!) or the Wine Rack, which would, since it holds 25 ounces of liquid in it's bra-shaped bladder, probably have some make-mom-look-like-Dolly-Parton properties :
Slightly classier are these fake lotion containers, which are actually very highly rated:
Happy Mother's Day!