Interesting post by Anythought and clearly supported by online links.
Vasculitis a possible diagnosis in the case of your Mum, but to put it into context,there are many types of Vasculitis and it is indeed rare.......I'm a general practice of 3,500 patients are doubt whether the doctor would see more than one case in his whole medical career, it is that uncommon. Your mother would have had blood tests which would have suggested such a diagnosis.
From what you have said in previous posts, a blood clot was never a realistic diagnosis.
Cellulitis sounds to be a likely cause and can lead to blistering which scab and can be difficult to treat.
Continue the antibiotics and reassess the situation in one weeks time.
Epaderm cream which can be bought over the counter massaged into the legs twice daily would help to moisturise the skin and is a useful antibacterial cream.
I,m afraid that mum is going to have to deal with this, despite treatment for many weeks if not months.