A.,
You're such a loving mother. Let me ask you a question. If you woke up in the middle of the night and your pillow was gone, would you be able to go right back to sleep? Probably not. I think what's happening is that you have become your daughter's pillow.
I try to remember that the only thing I REALLY have control of in my life is me and my behavior. Applying that principal to your situation, what do you have control over? Just you and your behavior. So, stop being her pillow! We all wake up several times a night but we've learned to go back to sleep. she needs to learn to go back to sleep on her own. The way you can help her do that is to allow her to fall back asleep in her room, without you!
You can cure her of this within a week or two at the most. She's old enough that you can reward her for every night that she stays in her room all night. Get some pretty stickers and let her put a sticker on her door for every night she stays in her room all night. When she gets five, she gets a party or Chuck-E-Cheeses or something. If she messes up one night, she can't put a sticker on the door but she keeps all the stickers she's already earned!
At bedtime, remind her about the stickers. If she gets up in the middle of the night (and she probably will at first) just silently take her back to her room and tuck her in (no kisses and hugs and stories etc.). Keep it business-like. Don't get emotional in any way. Keep it calm and quiet. Do this every time she gets up. YOu may quietly reminder her that she is to sleep in her bed all night.
I hope this helps!!!!!
S.