NOT A TEACHER
(1) Our wonderful friend Mr. Michael Swan (in his great Practical
English Usage) writes:
"In British English (but not [my emphasis] American), do can be used
alone as a substitute verb after an auxiliary verb."
The scholar's example:
"Come and stay with us."
"I may do."
Americans would never speak like this. They would just say, "Thank
you. I may." (So Americans would reply: She might.)
But "She might do" would sound very strange and funny.)
(2) Careful: "She might do" is American English in other
Mr. Jones: I am thinking of hiring Mona Jones as a model for
our fashion show.
Ms. Smith: Well, Mona is not that pretty, but I think that she
might do. ("do" in this sentence is NOT a substitute verb. It is
THE verb, meaning "to be acceptable.")
Student or Learner