You don't need a bargained away "detriment" for promissory estoppel.
In any case there's no need for detriment in promissory esoppel.
First of all, I didn't say "bargained away 'detriment,'" I said detriment
. A detriment does not require a bargain. I have no idea how you are defining "detriment," but if "an act or forbearance" induced by a promise isn't a detriment, then what the hell is?
Additionally, a detriment can also have beneficial effects for the promisee. Reverting to consideration-validated Ks: "I'll give you $10,000 to have sex with this woman." You have sex with that woman, she's hot, and you are hetero. You loved
the sex, but, guess what folks, in the eyes of the law, it's a friggin' detriment. You gave up your time to pay your taxes or walk around the block or whatever you usually do on a Wednesday night to screw this woman. It was a forbearance of your ability to do other things induced by an offer.
The only reason we refer to promissory estoppel as such is tradition and homage to Williston, who most likely coined the term. Williston on Contracts, Rev. Ed., Sec. 139, Vol. 1. "Detrimental reliance" is a much more descriptive and appropriate designation for the concept.
IF SHE ACTED in substantial and definite reliance on the promise, and the promise was one that the promisor could have reasonably expected to induce action on her part, then YES, it would be injustice for her to pay for her vacation.