No no I don't think it was the grim reaper per say .
I do believe she saw something out of the ordinary though .
In my honest opinion , all these supernatural events are related , be it grim reaper ,ghosts , poltergeists , or just plain weird sht .
I woke up one night sweating dreaming my father was being killed by a giant earwig , I shot straight up out of bed , and sitting at the end of my bed
was a large wolf like creature.
It looked very real to me since its eyes were glowing illuminating its body in the otherwise pitch black room .
I thought it was an evil spirt , demon , fallen angel what ever you want to call them .
So I said please God make it go away , and I threw my blanket over it .
And it was gone
Some people will say it was an hallucination , and maybe it was , but I still think your girlfriends story is related to my experience .
peace