She (the subject) ate (the action, and note particularly that the subject is performing the action) her dinner (the object of the action.)

Therefore this is the sentence in the active voice:

She ate her dinner around 5:00 pm.

In the other sentences, the subject is not performing the action.

Mrs. Reynolds (subject) was killed (by something which is performing the action.)

All of the bones (subject) were buried (by something which is performing the action.)

The truck (subject) was cleaned (by someone who is performing the action).

Here’s a trick. Think of what is doing the action. If this person or thing comes AFTER the verb, the sentence is usually in the passive voice. The sentence may not even tell you what is doing the action. If you don’t know, the sentence is probably in the passive voice.