Is this a console issue or a app issue?

Hi and thanks for reaching Microsoft Xbox gamer's community. My name is Josef.
I'm an Independent Advisor and a Microsoft Xbox user like you.

Hope you're doing great today despite this Emma

Additional information is needed, please tell me:

Do you have USB accessories connected to the console? (External drives, wheel, a keyboard, etc)
Is this happening only with Minecraft?
Do you have the game installed on the internal storage? Or did you installed the game on a external drive?
Do you know if Minecraft or the console received an update before this started to happen?
And, what Xbox console do you have?

Hi there, if you uninstall the Xbox app on your mobile device, power your device off and back on, and reinstall the app, did that help with the issue you're experiencing?

Also, if you try connecting to a different Wi-Fi network, do you see any difference?

I must say, really, really weird. Try
power cycle your console.

Try remove and then add her account again after that. Are you sure that you didn't changed something with controller on her account?

After having controller issues myself over the years, I wouldn't think that it was the console. If after going through the link that I originally included you don't notice a difference, you could try another controller if you have one. If the same issue
happens with that controller you could see about getting your console serviced.

I would remove her account and add it again just to see if that changes anything? Are you sure she didn't change any of the settings in the game that she is playing? Sometimes if you increase the sensitivity of the camera in a game, it might seem that
there is controller drifting.