Should I go for BOWP and try a shot at that authorization letter again or file her SOWP with my BOWP together?
Really wish I could suggest you something. But I'm no expert when it comes to immigration.
Best option as i see for you now is do BOWP and wait patiently. Having multiple applications PR, visitors and SOWP make it messy and IRCC end up rejecting both visitors and SOWP. Intent for SOWP and visitors is different from what i see. If our intent from these applications are not aligned, that might end up becoming a good enough reason for rejection.
If you plan for sowp, make sure you justice she has potential to find a job here with her experience letter, educational qualification, etc.,; + You being able to provide $ support until she secures a job. If visitors visa provide sufficient funds / means of funds (like inland residents employment confirmation, payslip) for support.
There are many expert immigration users in this forum. I suggest you get their insight rather than from me.