B.H.
My daughter did that exact same thing as does the baby I am now babysitting.
It's the bottle.
My daughter NEEDED her bottle to fall asleep. She got so used to it that she would wake up several times a night for it until I took it away at 2.5 -3 years old. I think they must like having something to suck on and a full belly or something. It was one of the hardest bad habits I've ever had to break. But once the bottle was gone my daughter stopped waking up several times a night. Also it's alot of unneeded calories when they're on the bottle past age1.They fill up on liquids and don't need to. I know my daughter was a FAT-Chunkie baby and most likely it was her bottle habit. She's now very slender and fit.
I'm now going through this with a little 1yr.old I watch overnight frequently her mom has her with the same bad habit and I'm at the point now where her mom has to break the habit or I can't watch her overnight anymore because I NEED MY sleep. She woke me up 4x on Saturday night and I was about to go bonkers.
The only thing that worked for me was to take it away from my daughter cold turkey. The first night was horrible the second night better and by the 3rd or 4th night not a big deal.
I did only give my daughter water but during the day she did have milk or juice and by age3 she needed 3 cavaties filled and her enamel was wearing off her front teeth. So we had serious dental damage from the bottle as well. Now my daughter is 6.5 years old and since the bottle has been gone we haven't had a single problem with her teeth since.
If it's not the bottle then she's got this habit formed of waking up. I would just let her cry it out. I don't even think you need to go in and rub her back or anything unless she's been hysterical for over 10min. or is sick. She's got this little game going where she knows you'll come running.