Hi Kristian,
Personally I would not rehome a dog with these character traits, a guard dog should be controlled and focused, not a set of teeth on a chain. At some point, this dog will bite someone (possibly a child) and personally I couldn't live with my concience if i'd rehomed it. If your mum wants to keep the dog I suggest contacting a good trainer and working through the dogs behaviour which sounds like a possible dominance issue.