HI, thanks for using healthcare magic
It is unusual for the labia to shrink in response to injury
. In the normal inflammatory response whether due to trauma or infection, swelling would occur.
The most common reason of decreased size is atrophy
that occurs in older women as they age.This does not occur as a short term response but over a period of time.
It would be best for you to visit your doctor for an evaluation. This would include assessment of any abnormal shape or size of the genitalia.
I hope this helps