Hi @Samantha r ,
>The 3rd node is not in the same domain. Does traditional log shipping work ?
Setting up the log shipping across domains is supported, and you can setup Log-Shipping on Database part of Always On Availability Groups.
If computers that are running SQL Server are placed in a multi-domain environment, Microsoft recommends that you set up two-way trusts between all domains that are involved in log shipping. However, if you cannot establish trusts between domains, you can use network pass-through security for log shipping.