I think BznsBuilder could be a perfect fit for your friend's needs. With its business rules and workflow automation, it can help your friend manage their business effectively without going full ERP.
I'd start here: https://alternativeto.net/software/microsoft-access/
If I were to really invest in dbms, and only able to read-only the data (analyze, query, etc) something like Metabase is my go to choice (https://www.metabase.com).
If I also need update the data itself, internal tools builder like Retool (https://retool.com) probably good enough.
But, it all depends on the use case.