J.S.
Once you do start co sleeping, it is hard to discontinue it. I do not think a big bed would work if her toddler bed is not working. Work with her by repeatedly laying her back into bed every time she gets up. She will then know what to expect next, that she will be put back into bed every time she gets out. Also there are some great little clips at www.toddlerbedandmore.com that anwers these issues and that may help. A lot of good tips on the web! Consistency is truly key in whatever you route you choose. Good Luck!