I'm slim, and when I only had a face pic, I found requests for full body shots annoying. I didn't like the implication I was lying about my body type. (Mind you, this was in the dark ages before digital cameras became common - I would have had to get a paper photo, get it scanned, etc. Now I have several full body pics on my profile, which solves THAT problem.)
Furthermore, even if a girl DOES send a full body pic, there's no guarantee it isn't from two years ago, before she gained fifty pounds.
My advice would be to limit your first dates to coffee dates. You can make plans for yourself for afterwards, so you have an excuse to leave. And, I don't mean you should bolt from the coffee shop the second you see her, if you don't find her attractive. It won't kill you to be kind and have a cup of coffee and a pleasant conversation with a fat girl -- you never have to see her again afterwards if you don't want to.
Also, you probably shouldn't accept a party invite from someone you haven't met yet. As you found out, you don't know what you're letting yourself in for when you do that.