Hi Helen,
There is really only one way to deal with this, and that's not to try and treat it yourself or guess what it is/isn't.
Go and get the "skin mass" checked out with a vet. Let's hope it turns out to be nothing much to worry about. Or even if she needs it removed, that doesn't have to be a terrible thing.
My dog once needed a lump removed from her lip, and biopsied.
It turned out to be an infected hair follicle. It never came back, but left a tiny scar on her lip where it had been taken off.
I have not idea what you are talking about - I can not visualize a "skin mass", that sounds bad but could be nothing but a sore.. how big, hard or soft... other description material may help.
Best to take the dog to the vet if the situation has not already improved.