This "authority" is in error; the past perfect is not necessarily required here, although there are circumstances in which it would be preferred in formal discourse, and the simple past is not incorrect, although there are circumstances in which its use would be deprecated in formal discourse.
This is in the first instance a matter of context— specifically, what you are trying to express and what time you are talking about, what grammarians call Reference Time.
Perfect constructions do not express events prior to Reference Time; they express a state grounded in prior events which obtains at Reference Time. So if you are talking about a time in the past when your subject's previous unfamiliarity with bears was of immediate relevance, the past perfect will be appropriate:
As she was hiking in the Tongass National Forest she was suddenly confronted by a menacing dark creature her own height and twice her mass. She did not recognize it—she had never seen a bear before she moved to Alaska.
But if your Reference Time, the time you are speaking about, lies before the time at which she moved to Alaska, a past perfect will not be appropriate:
She was in her youth a keen student of wildlife—kangaroos, wallaby, emus—but she never visited zoos, which depressed her, so she never saw a bear before she moved to Alaska.
In less cut-and-dried circumstances, usage varies: formal usage and British colloquial usage tends to employ the past perfect more often than US colloqual usage. If you have an appetite for technical grammar, I modestly recommend our Canonical Post on Perfect Constructions, particularly sections 3.2 and 4. If not, the best 'rule of thumb' respecting use of the past perfect is FumbleFingers‘ Perfect Truism:
”Don’t use the perfect unless you need it.”
Difference between use of simple past and past perfect depends on the context, e.g.
Simple Past: In reply to "Did you see your friend, whom you usually see every day, yesterday?" you might reply "I did not see him yesterday."
Past Perfect: In reply to "When did you notice your friend missing?" you might reply "I had not seen him yesterday."
Best Answer
is a more standard way to express the basic idea.
We would normally use never saw in this way only when there is a special reason to do so.
As Adam and gnasher729 point out or suggest, the reason for doing so is to communicate contrast.
For example, many prior occasions contrasted with none
Or a lengthy period in which I might have seen him or numerous opportunities to check or notice contrasted with zero sightings