"
Sharp words like knives, they were cutting her down
Shattered glass like the past, it’s a memory now
"Sharp words like knives..." could mean that every word that was said took a toll on her and eventually cut her down.
"Shattered glass like the past..." could mean that the past is broken like shattered glass and is no longer happy and it seems as there is no way to put it together or to make it happy again.