Oh keep us all informed! She may well be a terrier/cavalier cross or even chih/cav to get that small build, little head and all black colour -- I'd guess cavalier is more likely than cocker given the head shape and size but as always it is very hard to know (see my post on the cairn/cavalier mix who looks like a full cairn!).
Submission wetting often imrpoves very quickly with some training and as the dog's confidence grows, so I bet that will be fine. Otherwise it can always be managed so situations that trigger the wetting -- eg returning home to the house to the dog -- take place in a 'safe zone' like a tiled hall or kitchen floor where cleanup is easy. Most cases I have known of submission wetting have eventually gone away.
She is a very cute little girl and would make a fun addition to a group of cavaliers with her colouring! Also I think she would improve quickly in the company of some other dogs. Given that she has been through four homes now in a short period that will likely have exacerbated the weting too so bet some stability will help her very quickly too.