What does this idiom mean 'to be on a high'?

English as a Second Language English Teacher Explanations (ESL Tests)
1

Test No. [color=blue]incompl/inter-56 “High and Low”, question 1

She’s … a high at the moment because everything is going her way.

(a) in
(b) on
(c) for
(d) at

Test No. [color=blue]incompl/inter-56 “High and Low”, answer 1

She’s on a high at the moment because everything is going her way.

Correct answer: (b) on

Your answer was: [color=red]incorrect
She’s for a high at the moment because everything is going her way.
[size=200]_________________________[/size]

hi again, I’m back,pls explain the hole meaning.

rich7

2

She’s on a high = she is very happy.
Everything goes her way = everything is like she wants it to be.[YSaerTTEW443543]

TOEFL listening lectures: A lecture from a social science class (2)[YSaerTTEW443543]

3

Is this idiom English English? I’ve never heard of this before even though I can guess the answer easily enough.

4

.
It is familiar to me, and I’m AmE-- in fact, I think we might have originated it, back in the '60s. I’m not sure, though; my memory of those days is a little fragmentary.
.

5

Oh OK. Thanks…my circle of friends never used it I guess.