Had the girl seen full body pictures of you and your husband before? Not nude pics, but pics depicting body shape? Or had she only seen your face?
A week is not a long amount of time to get to know someone.
Secondly, people can and do get caught up in the rush of emailing or texting, because it doesn't feel real until you meet in person. There's a million reasons someone can drop off the face of the earth.
I had a girl last year messaging me all day, every day. It came to date night and she didn't turn up. I gave her a second chance, as she came up with a plausible excuse. She didn't turn up a second time. So I never text her again
She text every single day and what rang an alarm bell for me was that she'd occasionally start going down a sexual route... hinting that she would like a picture, or cybersex, or some such.
Even though I'd seen her pictures, she could have been a guy. She could have been a girl, with a boyfriend, who had no intention to meet. She could have just been a time waster.
Unfortunately, this does happen.
I've had the shoe on the other foot. I got a message from a woman who wanted a threesome with her husband. That's not something I've done before. I thought they looked nice enough and started to consider it. They were very pushy about setting a date and I ended up solidifying a date a couple of weeks in the future.
The more eager they got, the more nervous I got. I felt trapped. I didn't want to mess them around... but I was scared.
I went quiet for about three days while I thought things through and then messaged them to tell them I couldn't go through with it.
People do change their mind and people do tend to go quiet when they are having doubts.
The best thing you could do is ask her if everything's ok and tell her that if she's changed her mind, or is freaking out, it's absolutely ok to tell you. People don't know how to disappoint people.. so they tend to bury their head in the sand.
If you contact her kindly, and she is genuine, at least you can build something from there, if she wants to.
If she does turn out to be a time waster, or a fake, then perhaps take it as a learning experience and consider revealing yourself at a slower pace in future. I'm not saying it's your fault - I'm just saying that if you find that something doesn't work, it's always good to learn from it.
It is of course, entirely possible that she genuinely did get busy, too.