Yeah, I did notice that Jetta was created before DeCarlo started doing Archie...but if we're being nitpicky, Archie had nevertheless been around for some time before Jetta, so she was still kind of a ripoff.
I did already have a look at the Catalog of Copyright Entries, but I've only looked at the files for 1980, which is the year in which Jetta should have had its copyright renewed if anyone was going to do so. But of course I guess someone could have renewed them before that, too, right? Anyway, I'll have a look at this Ockerbloom thing, but it does sound like I'm in the clear (and yes, I did want to make my own comics featuring the character). Thanks.
One thing that did throw me off a little was that a company called "Airwave" did a volume that reprinted the stories, including at least one original story, a few years ago. Annoyingly, Airwave doesn't have a website, but I am trying to get in touch with them to make sure it was a public domain reprint. I'm also actually going to try and get in touch with the DeCarlo heirs/estate if at all possible, because I actually would like to send them some of whatever meager profits I make...I feel really bad for how DeCarlo was treated and I don't want to exploit his work if I can avoid it. Don't really know how to get in touch with them, but I'm digging.
Oh, on a tangentally related note, I did a comic for 24 Hour Comics Day that sort of points at the kind of thing I'd like to do (though this is much goofier). You can see it here:
http://s1.zetaboards.com/dcg/topic/2374246/1/#newAnyway, thanks a lot for your help!