Considering this is really bothering you right now and it is very upsetting, I would reach out with a kind jester. Making her a cake, some cookies or even giving her a plant can break the ice and get the two of you talking again. You have explained the problem so well here in your question, I feel like you can use this to start the conversation with her. You can knock on her door and offer her a kind jester and explain how bad you feel over the argument that you had. Let her know that you are a bit overprotective of your granddaughter and you are so sorry that it got in the way of your friendship. Let her know how much you miss talking with her and how you wish this could all be put behind and you could be friends again. I'm sure she will have a real soft spot in her heart when she sees that you have brought her a cake or even cookies. She might even invite you in to have coffee with her and share a piece of cake. I had disagreements with good friends and even though I was only defending myself and they got angry, I have reached out to them with a kind jester so we can talk again and it is a good icebreaker.