You don't have to trust the coordinator in WabiSabi.
Can't the coordinator simply choose to put me in a round where there is only their and my coins joined?
However, explain why wouldn't Alice double register ("Mix with herself") in this scenario?
I meant that your premixed coins are not going to be mixed in the same coinjoin. Each premixed coin will be mixed in separate coinjoins. They might share a coinjoin only if they are remixed.
However, I don't want to play it smart. I have not studied the whirlpool protocol, and that's all I interpret from simply reading a summary from their Telegram and Twitter accounts.