Every day, she manages to escape into the backyard as the kids are traipsing in and out, and I let her stay out for a while. Eventually she comes to the door and we let her back in.
At about 11PM, we put her to bed in the laundry room, where her food, water, and litter box are, and we let her out again in the morning. This she intensely despises, although tonight she only scratched at the door for a little while before she gave up.
Since we started this routine a couple of days ago, she has consistently used the litter box.