At 19 many young people are stepping away from childhood and becoming adults, for some this move away includes distancing themselves from family and those who remember or are associated with their childhood.
However this stage is rarely longlasting and within a year or two they turn back towards their family.
There is a quote, variously attributed to Mark Twain, Oscar Wilde and other witty hmourists . It goes:
When I was a boy of fourteen, my father was so ignorant I could hardly stand to have the old man around. But when I got to be twenty-one, I was astonished at how much he had learned in seven years.
So your granddaughters behaviour is recognised behaviour for young people of her age. And, yes, I am sure her difficult family circumstances will exacerbate the problem, but she will return, so do not overeact, stay tranquil, as the French say, let her know you are always there for her and then let her be. She will return.