She's at the age to pay attention to people and react to what they're doing or not doing. You have to wonder what is going through her mind. Please tell Grandpa to be very patient and not take her current rejection of him personally. Ask him to continue to be friendly to her and allow her to stay at a distance. She will come to love him and play with his beard again, but it may not be tomorrow or next week.
My granddaughters all did this to me at one time or another, and I don't even have a beard! They really wanted nothing to do with me. It was hard not to feel hurt. But I still saw them, smiled, talked gently, let THEM decide to come to ME... and sooner or later (I had to be patient, too) they decided I was acceptable. I wonder if I'll still be acceptable when they're teenagers... but that's a whole different matter.