Is a tourist visa renewal ideal?

My girlfriend has had a U.S. tourist visa for almost 10 years, and it's about time to renew it. On her last visit to see me in the U.S., she stayed for almost the full 6 months and left right before the date she was required to leave. At the time, we genuinely thought that as long as she departed before her authorized stay expired, everything was fine. We didn't realize that staying for the maximum amount of time could raise concerns, even if it's still legal.

We've now been staying in Brazil together for about a year, and we'd like to visit my family in the U.S. again. Since her visa is close to expiring, we're a little worried that her previous 6-month stay could affect her renewal or future entry.

A lot of people tell us to just get married and apply for a green card, but that's not really what we want. We'd rather continue visiting each other without making such a major legal commitment just for immigration purposes. The only reason we'd even consider it is if it genuinely made travel significantly easier, but if our goal is simply to visit family and spend time together, shouldn't a tourist visa be enough?

Has anyone here been in a long-term international relationship where you traveled back and forth for years on a tourist visa? How did renewals and border crossings go? Did long visits cause any issues, or was it okay as long as you could show strong ties to your home country?