Involvement in Fallout 4
Following River's passing, Joel Burgess made a Twitter thread writing about how she came to be involved in Fallout 4. Originally, the team researched "professional" dogs that had film and/or police training to serve as the model for Dogmeat. However, they found images of German Shepherds snarling and in attack postures to be unhelpful. They wanted a companion first, and a combat ally second.
River soon started visiting the Bethesda studio and attended several meetings. However, her main job was not just to serve as a reference, but to be with the team. The group of developers working on Dogmeat's functionality was initially quite small, though other developers soon began to pitch in, wanting to help bring River's personality into the game, greatly influencing Dogmeat's appearance in Fallout 4.
Dogmeat's brown eyes are replications of River's own eyes, and Dogmeat's tendency to trot ahead of the player character, then look back, was something that River did on long walks. She also had a habit of grabbing large objects such as sticks and bringing them to the team to try and make them happy. This influenced Dogmeat's item-fetching and seeking behavior, which was developed by Jon Paul Duvall and Jay Woodward, among others. Dogmeat's focus on holding enemies in place, rather than direct damage and finishing moves, was also a character choice inspired by River.
River was a patient and gentle dog, which helped the team significantly when gathering references for foley and modeling. The team specifically wanted to avoid using stock libraries for Dogmeat's voice, and the recording sessions for audio were often tricky, but ultimately worth it. Joel concluded the Twitter thread by stating that, ultimately, Dogmeat is a tether who loves you, and if love was River's legacy, Joel would be content.
River in Fallout Shelter Online