I study English I don’t understand this sentence:
"I think most of you have probably received a tin of her cookies over the years"
Why someone used Present Perfect?
There are lots of situations in English where speakers could choose either the present perfect or the past tense, and the construction would sound idiomatic. This is one of them.
Your comment that the woman concerned had since died makes it likely that many speakers would have used the past tense. It's the phrase over the years that's really the key.
The speaker is drawing a time line from the point when people first began receiving her cookies up the present. Even though the woman has since died, the speaker is aware that she has just died. And the sentence is constructed as though her cookie giving has continued up to the present moment.
So while it's natural to say:
I think most of you have probably received a tin of her cookies over the years
The tense would change to the past if the context changed.
I think most of you probably received a tin of her cookies last year.