I could be very wrong, but I would imagine that female canon lawyers have been allowed as long as lay men have (from a Church point of view)
The only time the sex of a person comes into play is for ordination & minor orders (plus you can’t marry someone from your own sex).
So as long as lay canon lawyers have been allowed, there would have been no reason not to allow female ones. Now, that doesn’t mean women have been actually doing as long as lay men, but technically, there shouldn’t have been anything preventing them.