I have to wonder if there was some sort of family fight going on about Paula's ashes which LW was too young to know about or carefully kept away from, such that either a) some of Paula's ashes were scattered and some were kept or b) some family members were not told that Paula's ashes were scattered, and led to believe this random urn was hers. I find both of those reasonably likely, but it seems odd that someone who worked at a crematorium wouldn't consider them!

The only other option I see here is that at some point someone was clearing out a relative's stuff who wasn't close to Paula, asked what the urn was, somebody else said "idk, maybe Paula?" and it became gospel among the part of the family who hadn't been involved with Paula's death? In which case I'd wonder if it is actually some other distant family member.