Thank you all for your replies. I decided to call HAL late Friday afternoon. I explained our situation and stressed that we did NOT want a refund, or future cruise credit. I even said we don't even care if we ever see her port fees or onboard credit. The woman joked that this was something she had never run across as most people want their money back.
She spoke to her supervisor and I was instructed to email my sil's Statement of Death, and then one day this week (just to give them time), call the Documentation Department to access my mom's boarding pass. The woman spoke to two different supervisors to make sure my mom would not be charged extra since the cabin was fully paid for and we want nothing back.
This morning, I logged into my mom's account and although my sil's name is still on the reservation as well, my mom's boarding pass box was active and I had the paperwork emailed to me!!! Success!!! With all of the reports of airport chaos, I can now relax knowing my mom will not be denied boarding.
FYI - my husband and his sister were going to toss their parents ashes on this cruise (in biodegradable boxes) as they were avid HAL cruisers in their day! Now he will be doing it himself. (Yes, we have notified HAL already!)
This will be our first cruise since covid shut everything down. We are very excited to be cruising again, even though this cruise will have us thinking about three deaths from his family. It will be a celebration, as we all love cruising! I will post about his parents ashes when we return from our cruise - middle of August.
Thanks again!