How do you know if your phone is hacked?

I've been paranoid since when my cousin showed me the YouTube video that I'm watching on my phone. I'll make it short. I showed her the video because she wants to see it. She then took her phone out, the camera was directed to my phone. She asked me again to show her the video and I did. She then pull her phone and started tapping somehing. It took her I think less than 20 seconds and then showed me the video that I showed to her.

It wasn't actually the exact video, it was sort of because they were in the same room. She got the latest iPhone 11 tho.

She probably used her camera to search it up because when I showed it to her, her phone's camera was directed on the video that I'm showing.

Idk but this made me paranoid since.

Plss I need answers..