Watch App crashing while activating grandmother's Apple Watch Series 3

My grandma gave me her Apple Watch S3 after she decided she didn't need it anymore. So I erased the watch through settings on the watch, and I removed it from her Apple ID. Now when I attempt to pair it with my iPhone, once it reaches the, "Activating Apple Watch" section, it crashes. Its been continuously doing this everytime I attempt to pair the watch. I've tried to restart the Apple Watch and my iPhone but nothing seems to work.

[Re-Titled by Moderator]

Original Title: Watch App crashing on activating watch.