I would send her a Christmas card and just say 'I'm so sad not to have heard from you. Thinking of you and hoping all is well with you'. Without knowing her and you it's impossible to know why she has done it.
Maybe as others have said she just needs some space to grieve. Personally if I was in her shoes I would want to be on my own for a while to get my head together and decide what I want to do with my future.
Not everyone thrives on well meaning friends and sympathy. Someone once told me I was like a wounded animal when I was hurting, I would creep into my burrow until I felt better and able to deal with the world.
Making unwanted threads move down the list out of sight
What is a reasonable minimum spend for an online grocery delivery??
Being quizzed by chemist's assistant in Boots.