After looking that up, I think it may be a female tarantula hawk - "Pepsi Thisbe"

female, yes. i am afraid i do not know of or have a good key for Pepsis... i think Townes may be a little out of date. also, i believe it is often difficult to tell these apart with pictures alone, and there are very few in my area. in any case, here are some of the possibilities... you should have at least one Hemipepsis, H. ustulata ustulata, and a number of Pepsis species... P. angustimarginata, P. chrysothemis, and P. grossa, probably not limited to these, but all of these look rather alike. i am not sure if thisbe makes it to you, but it is very possible. in the end, i am not sure i can see the things needed to key this well, but perhaps Nick Fensler will see this and be able to do better than i.

Yes, this is definitely a female Pepsis but not P. thisbe, that's a Sonoran form. Could be P. grossa, P. angustimarginata, P. chrysothemis lucasii or P. elegans cerberus (I'm not sure if that's a valid subspecies after Vardy's revision, I don't have that literature). All four of those species are orange-winged with a black flagellum and are found in Oklahoma. Most of the other species of Pepsis are tropical and therefore found substantially south of Oklahoma. Pompilidae are very tough to ID from photos.

is there anything out there to key Pepsis other than Townes (which i found an actual copy of online and was very happy about)?

Unless you can get a hold of Vardy's recent revision there is only the old revision by P.D. Hurd and Townes, the keys being essentially the same.

P. chrysothemis lucasii was synonymized under P. chrysothemis by Vardy in 2000.

As for P. elegans cerberus, I'm not sure about that name. P. cerberus is a species on its own, so perhaps it was elevated from subspecies (not sure when).

I wish Pepsis were easier to ID by photo.

Most subspecies in spider wasps are rather frivolous and in the guide I rarely make a page for a subspecies unless I consider it to be truly a distinct subspecies. For instance I do not recognize the subspecies of "Calicurgus hyalinatus" (=the valid Caliadurgus fasciatellus) since I (and another biologist) have found three of Townes's "subspecies" sympatrically. I don't like subspecies anyway...it's often too tough to tell where to draw the line. Probably the case with P. chrysothemis.

P. cerberus IS a full species and apparently has been for a while (can be found in Krombein et al. (1979)-the Hymenoptera Catalog. Evidently someone thought this former subspecies of P. elegans was distinct enough to be named a full species but I don't know whom, and the lit. isn't listed in the Catalog. I don't work with Pepsis much at all since none are found in Ohio (one very old record of P. elegans), so I guess I had just forgotten about that one.