I forget the last time I logged in using that account, because as far as I remember I only opened the Sherbet site when registering and never opened it again.
If I'm not mistaken, I registered while their campaign was still running. I was interested to registering because I think Sherbet is a new casino so it usually has good bonus offers
If I want to deposit, I will try to ask live support about this problem
To be on the safe side, it would be better if you tell Sherbet about this. If ever your account get banned because of this multiple accounts, you will tell this whole story to the Sherbet support, won't you ? So i think it will better if you tell this story to team in advance and hope in this way, they will not close your account and you will not have to face any unforecast issues which may arised in case you hide these facts.
Other than this, i think there is nothing to worry about it and Shetbet hopefully won't be upset about your logins as you have a geniune reason for your actions.