Okay so I have two ideas on what Coco's semblance could be. One is that she has super strength. It would easily explain why she is able to cause so much damage with one swing of her purse thing. It also helps to explain why she can use her Gatling gun like thing. I could be wrong with the type of weapon she has. The other idea is that she has something along the lines of a "lock on" like ability that helps her aim.

Can not take all the credit for this so thanks NiallHeffernan for the strength idea.