past perfect continuous questions

Point 87 in the category of PAST:

past perfect continuous QUESTIONS

A search in COCA:

1 HAD SHE BEEN THINKING ? 23
2 HAD HE BEEN THINKING ? 18
3 HAD SHE BEEN DRINKING ? 8
4 HAD I BEEN THINKING ? 7
5 HAD YOU BEEN DRINKING ? 4


EXAMPLE:

What had she been thinking?