Having seen this stuff many times in my travels, I completely agree with Virg. The reason that they print the price in a tiny font is to take advantage of people who are naive about this. If they were being honest, the would print the price so that it is easily visible. This is why there are product labeling laws and other laws that prevent "fine print" that changes the value of the deal. Yes, a consumer should be careful about what they consume/buy/sign, but they shouldn't have to carry a magnifying glass to inform themselves.
From the description in the OP, it doesn't sound like the size of the font is the real issue. In fact, it seems to have become a bit of a red herring. According to the OP, her DD walked in the room, grabbed the bottle and immediately opened it. She didn't say that her DD paused for even a second to look at the tag, just that she picked up the bottle and opened it. How large should the wording on the label be to attract the attention of somehow who doesn't stop for a moment to look at the label in the first place?
I remember the first time I saw a bottle of water in a hotel room that wasn't in a mini bar. I thought "cool, free water." Then I saw the tag, read it without using a magnifying glass, and realized that it would cost me money. So I thought "darn, stupid hotel!" And I didn't open it.
Okay. We're getting nit-picky here. Maybe she did read some of the tag, maybe my back was turned. Even so,
I couldn't read the fine print without my reading glasses.
Do you honestly read the fine print on the bars of soap that they leave for you in the hotels?
I'll agree, perhaps "rip-off" was not the proper term to use in my title.
I'll also agree that the fine print is a bit sly and underhanded. I would guess that it's been 5 years since I've stayed at a hotel. Plenty of posters have said that they, too, were taken in by this tactic (or might have been if not for this thread.)
I agree with the others who said there's nothing sneaky about this, just a lesson to learn. IIRC, your girls are in High School and College/Beauty School, yes? That's old enough to "look before leaping", so to speak 
Yes. They are old enough . . . but, but, but I'm 50+ years old! What's
my excuse? Oh, yeah, I've never run across this situation before.

Yes. We did learn our lesson (see my OP.) We did have fun with reading the fine print on
everything. So I'm betting that this lesson will not be forgotten.