I agree, what would a t-shirt accomplish? I mean it's cool and all, but I don't see other SIGs making a t-shirt for their events.
Regarding what we do, I think it would be a great shame if we all sat there quietly watching a film, I can do that even when I'm not with a bunch of furgirls. I'd rather talk. I know that we're not allowed snacks and such if it's in a public room (unless they are bought from the hotel), but if we turn it into a pajamas-style event with pillows, blankets, whatever we can find and just sit relaxed and talk informally then I think it would be a nice and cosy event. Perhaps you could prepare a couple of questions or topics to get it going? That's what we did at Anthrocon and it worked really well. Well that's just my opinion and suggestion really.
I'm not sure if sending out yet another update, this time specifically to all female attendees, is the best way to approach it. Some might get annoyed with what they could consider "spam advertising". That's of course up to you to decide Sinea. But I can offer something else: I could briefly mention it as one of our new events during the opening ceremonies. Then all the females who are actually there will hear it. Would you want that? (Don't worry Cheetah I'd keep it super-brief, I know we have a time limit).
...it really is a shame we can't stuff ourselves with sweets and cake