Photo shoots don't require a theme. Maybe it's just semantics but that word seems so gimmicky to me.
I will say that any shoot you do should benefit your portfolio to some end. What is yours? Agency representation? Artistic images, great FB stuff...? All those require different approaches.
If the work is for your portfolio to promote you and obtain work, it doesn't need a theme. They just need to be quality images that best represent you as a model. It's not terribly creative or exciting but it's effective.
If it's just for fun work then I would think the photographer contacting you would have some concepts in mind. I've never worked with a model I've contacted and expected her to come up with some fantastical theme for the shoot.
Michael Pandolfo wrote: Here's my theme. We're going to take some usable images for your portfolio. It will take no more than 2 hours, shot on location. Don't wear stripes and leave the boyfriend at home lol.
So the model shows up in her prom dress... and the location is the beach...