You know what, I definitely want this OC to be a woman now. Let's fill the story with women characters since DD gives us so little!

Could she maybe be someone Fisk(/Wesley) sends to seduce/incapacitate his adversaries? Maybe not, for an assassin/spy hearing would be important.
So maybe "just" to have her serve at his business meetings, much like Matt. They could be the only ones allowed into the meetings, and would also have to clean and prepare the rooms where the meetings take place (?).

So Matt and this OC would have a role beyond being a stock-asset, just a very specific one that would leave them with a lot of time on their hands.