Signs that I'm truly patient

[Nitro Zeus]

I have a Christian grandmother who really loves to create problems to us all, and the way she talks, it aggravates me a lot that I feel like wanting to yell at her.

Now for example, when she has caused a lot of irritation to me just because she didn't know how to utilize her smartphone, and she had smartphone for very long time and still did not learnt how to utilize and this what makes me angry because I was hoping that she would be learnt by now how to utilize it. When she caused a lot of problems, I have not yelled nor have acted upon my anger, and I tried to ignore her.

Is by having a big trouble maker relative like her, it is a way in which God tests my patience? And if I try my best to be patient, then would God erase my sins even disbelief and He would reward me in Hereafter for being patient?

P.S. The reason I have included disbelief, because sometimes I fall into it because I am an extremely weak Muslim. But still I do truly believe in Quran, because that's how I feel and I cannot deny that. Please don't judge me. My grandmother is very annoying and evil, she was like this for whole life, and it is hard for her to be changed.