Question: Did you give that Companion specific instructions about where to meet when you get separated? It's one of their dialogue options that gets often overlooked.
Try looking in all other tents and bases to find her. I assume you already checked your Party Points with the ~pp command to verify she's still your follower.
Beyond that, i believe there was a long-standing problem in the past with disappearing Companions and i don't know if they ever fixed it, but don't give up. I sometimes use Companions but mine rarely die, so my experience with this is limited but i have always found mine when it happens. There have only been two times when they showed up at a weird location that i would have never guessed. It took me a while to find them - i had to systematically visit all of my tents and bases.