Rebecca “Becky” Vance had an irrepressible urge, a genuine need to get away. Despite little preparation and with amateur outdoor survival skills, Vance, 42, convinced her sister Christine last summer to “live off the grid” with her and her son in rugged western Colorado, leaving behind their lives in Colorado Springs. Becky — said to be an anxious loner further exasperated by society during the pandemic — wanted to start anew by fleeing into the wilderness, where extreme weather and other potential pitfalls awaited in the Rocky Mountains. But she couldn’t be stopped, her stepsister told The Post.