I think my mother has the key to my iCloud account
what can I do to prove it and that she has been hacking into my phone because she has the key
what can I do to prove it and that she has been hacking into my phone because she has the key
There is no "key" except the password. And if you think she knows the password, then change it.
Otherwise, can you provide a bit more information as to what makes you think that something nefarious is going on?
GB
What to do after you change your Apple ID or password - Apple Support I suggest doing this before you change your Apple ID or password.
I think my mother has the key to my iCloud account