Board Thread:General Discussion/@comment-87.102.2.235-20160720090052/@comment-4010415-20161013025518

Nikoli the rebel wrote: she had likely been up against every known form of Grimm or at least had studied them all to know there weaknessess. WoR: Grimm said new types of Grimm are discovered all the time.

Also, never forget, everyone makes mistakes. Even professionals screw up or have an accident once in a while.

That, and one of her lines in Red Like Roses Part 2 is "I didn't have a choice. I did what I had to do. I made a sacrifice but forced a bigger sacrifice on you." So, it seems that, if this song is right, Summer was backed into a corner and had to make a sacrifice, and that's how she died.