Am I in the wrong?

iluvuangel
My grandma and I have never been good at communicating with each other. While we share some good moments there are also some bad moments which I feel weight on everything good. Whenever there’s an argument between us I feel like she isn’t mature enough to talk to me about it like an adult. I’m just a teenager and I feel like I’m forced to think like an adult. I just want to have a normal discussion with her, but she talks behind my back to my cousin or other family members putting me in a bad light.

This has been a reoccurring problem for months now. She’s very sarcastic with me and talks to me in a condescending way.
This time the argument was about money.
I get allowance every month and it’s $100. I’m aware it’s much but she expects me to use that money on basic needs such as new clothing, jacket, shoes, food and so on. In todays economy that’s not enough for all that and then I also don’t have money to buy what I want. I asked her to get some cheap headphones for my exam which was about 10$. She refused and told me to use my own money, but I disagreed and told her it was her job to provide for me also since that’s what she signed up for. The argument became pretty heated and whenever I tried to come with my opinion she would scream “lies”. Of course I was upset about the whole thing and I said some things too, but overall, am I in the wrong?

Keep in mind, this is not the first, every single argument doesn’t have a good outcome and I feel like she never admits to her wrongs. I can be pretty stubborn as well, but if I know 100% I’m wrong then I’ll apologise.
She spends about the same amount of money on my cousin, but she doesn’t have custody over her.
Updates
4 mo
Arguments like these aren’t all about the same topic, sometimes it’s about favouritism when it comes to my cousin. She’d claim I’m just jealous and she doesn’t take my mental health to account. When I try to talk to her about issues I have with her in a proper way she sees it as a personal attack.
It’s very complicated but I try my best.
Am I in the wrong?
2 Opinion