Ma'am would be an incorrect prefix for a female Knight. Ma'am is said to be polite not respectful. The proper term would be Lady, and the L should always be capital.
From a dictionary:
1. Lady (initial capital letter) (in Great Britain) the proper title of any woman whose husband is higher in rank than baronet or knight, or who is the daughter of a nobleman not lower than an earl (although the title is given by courtesy also to the wives of baronets and knights).
Of course, there were no female Knights in the historical past, but considering the definition I'd say it's fair to assume that is what they'd be called.
So, for example, once and if AkiroChan achieves status as a Knight, subordinates would address her as
"Lady AkiroChan".
