Unable to change account

My sister logged onto my ps4 to play overwatch but then she bought a copy for herself on Xbox. But now I’m unable to change into any other account I have

This sounds like a linked BattleTag conflict. You may need to create a seperate BattleNet account for your sister to link a console account to and then use yours for yourself. I would also note, per the End User License Agreement, account sharing is not permitted.