Hello @katonline and welcome to Mayo Clinic Connect. You will notice that I have moved your post into an existing discussion with members who are connecting on the very topic of vaccine hesitancy and why to or not to vaccinate. I thought this would be a good match given your introduction so that you could more easily connect with members such as @sueinmn @estrada53 and @loribmt who have all been active contributors.

The following resources do a good job of explaining how antibodies and the different vaccines work.
-Antibody Testing:
https://www.mayoclinic.org/tests-procedures/covid-19-antibody-testing/about/pac-20489696
-Comparing Vaccines:
https://www.mayoclinic.org/coronavirus-covid-19/vaccine/comparing-vaccines\
The biggest difference between the antibodies versus the vaccine is that in order to have the antibodies, a person must be infected with COVID-19. With that, come the varying degrees of how sick they may get and the complications that may arise down the road from potential "long-haul" symptoms as a result.

Has your friend tested positive for COVID? What is his/her greatest concern/hesitancy with the vaccine?

Her is the answer, direct from CDC. The shortmanswer is that the vaccine teaches your body how to react to the virus, in a more general way than the after-virus antibodies, which confer immunity to the specific strain you had for an unknown period of time. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/vaccine-benefits.html
Sue