。
Over the years, she wore down the kitchen knife.
Literal
She [topic-は] long-years [possessive-の] during [in-に] kitchen-knife [object-を] wore-down.
すり減らす ('to wear down by grinding/using') is a compound verb: する (to rub) + 減らす (to reduce). 長年の間に ('over many years') sets the time frame. 包丁 ('kitchen knife') is the standard word for a cooking knife. The sentence captures a quiet, domestic detail — years of daily use gradually wearing down a blade.