Is it okay for me to still give my baby a bottle during the night?

My girl is nine months old, and she's been having ridiculous sleep problems. A while ago, she would sleep through the night without a bottle. Recently, she's started waking up a few times a night and then permanently at 6am. I found that if I give her four ounces of formula, she'll sleep until almost nine. I'm a little worried though because I've been told that they should be off of middle of he night feedings by five or six months.