I'm not sure if 4 months is too young with co-sleeping. I know it's not too young when they sleep in a separate bed, but with co-sleeping, they wake up, know you are there, and then learn to use you to get back to sleep with your help.
If you want her to learn to get back to sleep on her own (waking up during the night is natural for everyone), then you'll probably need to first get her to sleep by herself. If this is something that you want, I would check out Good Night Sleep Tight and/or the Secrets of the Baby Whisperer. Both which I have first hand experience knowing they work. They are built on the routine of the Babywise book, but have a gentler approach to teaching your child to sleep on her own.
If you are committed to a family bed, then I would read more up on Dr Sears and Attachment Parenting philosophies to see what you can expect from this approach. (I used the baby whisperer and my son was sleeping 11 hours a night by 16 weeks....)
Finally (I know I've recommended a lot of books)I would also read over Healthly Sleep Habits Happy Child--by Dr Marc Weissbluth. He is the child sleep Dr. and this book explains how much sleep children need based on age, how many naps, how long, etc. He has done tons of research and everyone (including Dr Sears quotes him). And he doesn't advocate any methods--CIO, Family bed--but instead gives you info based on all approaches.
It's really about what you want long term, and the kind of parenting approach you want to take. Good luck!