Hello Katie, welcome to TBN. Sorry for your loss.
I know nothing about a Bolens of any model, but others here certainly do. It might be helpful to them to know the approximate vintage of your mower or a model designation.
There must be some lever, knob or switch that is marked as the PTO (power take off) that would engage the mower. Usually, the engine won't even start if this is engaged. Newer models frequently have an interlock that turns the mower off when you start to back up (usually an electric clutch is used for this).
Do you have an owners manual? It would be explained very well in the manual. Good luck and again, I'm sorry to hear of your loss.