Oof - this is a tough one! I'd say "it depends".
If it was just a relative re-posting a few pics, and/or if those pics featured the relative (for example, if Aunt Harriet re-posts three pics from 50, and they all feature her), then yes, I think the LW is being a bit precious.
But if these relative are re-posting whole swathes of photos, or these photos don't really feature the relative in question, I can understand why the LW is feeling a bit miffed - especially if they have some extra degree of artistic quality to them.