This is old, old etiquette. From the early days of restaurant entertaining, when people were genuine hosts (especially when ladies didn't handle money).
It's also useful today when people are genuinely hosting; though sometimes what's arranged is a custom menu, where the expensive things the host doesn't want to pay for are not included on the menu, but prices are left off.
And I think Dad was the source of the problem.
only to be given a stern look from her dad and thus divining it was too expensive and she would have to pick something else
Because if he can't afford to pay for the entrees at that restaurant, he should have picked a different restaurant. Or ordered something less expensive himself to make up for it.
And "stern look"? C'mon, Dad, nobody needs to be scolded here!! Just say, "Oh, you know, that one's $20, all the others are $15, so don't order that." Stern look? Insert multiple eyerolls here!!! (did Dad know that her menu didn't have any prices?)
Or, he should have shown her the menu with prices, or said, "don't pick the steak, the lobster, or the veal, because it's too expensive."
I think she should have gotten up, gone over to the maitre'd, and asked for a menu with prices.