Here’s something you can do. I lost my grandfather this year so this is what I plan to do:
If you can, prepare an altar like @Abs53 Abs said, especially if you have something that she gave you. There are more ideas for Ancestor Altars here.
I’ll start with flowers, fresh water and coffee, but depending on what your grandmother would like: tea, alcohol, tobacco, bread, etc.
Light a candle and say a prayer, something like this can help: Wiccan prayer for the loss of a loved one.
You can write your own prayer asking for protection or guidance. Tell her that you welcome her communication and thank her for the sacrifices she has done for your family. 
You can also talk about your life, or write a letter to her telling her what’s going on in your life. While doing this, you’ll feel very present and you’ll probably get more ideas based on what you know/remember about her.
Meditate. If you have time on that night, go into a deeper meditation than usual and see if you receive any specific messages, or dreams.
After that, no matter if you receive any signs, simply keep exploring your ancestry, look at pictures, explore your DNA, or dive into lucid dreams to try and contact your ancestors.
Edit: Adding this guided ancestral meditation that Kira recommended: Meditation recommendation and chakra mist
Best of luck!