You can't get over that and nor should you have too, it's okay that you don't.
You were dealt a fucking horrid hand with losing granddad in such a horrid manner.
You had someone who for some reason was trying to ruin you and we can bash it out as to why she did it, but you may never know, she did it and its fucking painful and I'm sorry that happened. Absolutely shite.
What you do now is you accept it, learn to live with the fact somebody betrayed you and you feel gratitude they're out your life and now you work on new relationships with kind people.
We all want to get over things but we rarely accept we can have a good life without healing from trauma, sadly that's not always possible and you just have to, every day, when it hurts, think of how rich your life is without her and be grateful she caused some damage, but didn't do anything that ended without you being here.
You encountered a very fucked up person who was toxic and jealous and had some evil in her, but she's gone now.
Youre here and will have a fabulous life.
Each day the strong feelings of hurt will lessen until its not as painful, it'll always be present, accept it, but remind yourself it won't define you, it won't ruin your day if you think about it and there are 7bil humans on this planet, you have the opportunity to seek out lovely ones.
Feel excited for your future, but be careful with your trust, use her twattishness to give you a guide for what to see as red flags and what you won't accept.
It's tough but you'll have a better life for adapting your attitude x