You're not thinking of the various novels involving Bernice Surprise Summerfield & Clarence are you?
Aside: I have one of the books (Where Angels Fear) but I hadn't realized until I Googled her name just now that she was originally created as one of the Seventh Doctors companions, the books are a spin off of Doctor Who.
Clarence is an angel, he was a battleship but his "body" was destroyed so "God" crammed what was left of his mind into the organic body of an angel, possibly (at least partly) as a practical joke, he's lost most of his memories from before his old body was destroyed.
God is the name of the AI that serves as the government for Clarence's people, all of it, all by itself, it's essentially a benevolent dictator in chief with CCTV surveillance literally everywhere.
Clarence definitely has a thing for Bernice so that fits, as does the angel with memory loss & also the crashed (or rather destroyed) ship, just that the angel & the ship are perhaps the same entity.
Working against the possibility this is what you're thinking of is that she's a 26th century girl, which wouldn't seem likely to be very "low tech".
But that said she was a Doctors companion & I've no idea where (or when) the Doctor left her when they parted, so that could have been anywhere (or when) & Clarence could have come along after she left the Doctor, so it could still be the one you're after?
I'm sure you'd have remembered any reference to the Doctor so if this is what you're after it must be from those of the Virgin New Adventures series published from 1997 onward that he's not in.
Having checked, Clarence first appears in Ghost Devices which is post Doctor.
Here's a Wikipedia List of Bernice Summerfield characters that might help you figure out if this is it.