Why is my dog afraid of everything?

Ok so i got this 4-6 year old female beagle and shes afraid of everything no matter how nice you are to her whenever you enter the room she runs away and growls, she pees and poops on the carpet and she has mental fibs, there's something wrong with her brain, one time my dad sat on the top of the stairs and the dog was in the basement so when she comes up its like halfway up the stairs then growls then goes around the basement then comes back up and then she did that 130 times im not kidding, every time my dad comes home she paces around the table, and when you walk past her she thinks your chasing her, we never did anything to her, we think her last owner* (we don't know who it was because she was in a shelter and she has no records) *got fed up with her and took her collar off and let her go... we don't know what to do with this dog so any advice appreciated