We use a step in for Annie as well and its the best. We had originally got her one that you had to put face through and that was always a struggle. But this one is great. I little pricey for the Harness and Lead, but worth it for something you will use daily. It's really durable.
Here's the link of where I got it from:
http://trixieandpeanut.com/collars/nylon/uc3160.html