I did the Ferber method when she was about that age, and it works. It is more hard for the parent than the child. We have to still do it once in a while to 'reset' her sleep cycle after coming back from out of town.
Babies learn very, very fast. They are smarter than you think. They know that crying causes mama's attention. If you give in, they learn really fast that crying will bring mama back.
Contrary to what others say, Ferber method is NOT traumatic and it WONT make your child grow up to be a serial killer or some other crazed chick. Do you personally remember crying when you were 9 months old? Are you a serial psycho now? No, and she won't be either, because she won't remember the crying later on. Even the next morning, she'll greet you with a happy smile, as if the previous night's events never happened.
Yes, be prepared for crying. It can last hours, but DO NOT give in. The first night is the WORST. I busied myself with checking email, or doing housework.
After that, it gets better. By 4 days, she will be trained. For some, it can take up to a week. Depends on the baby's temperment. If she is a very strong-willed, stubborn girl, it may take longer. Especially in your case where she is waking up 2-4x a night to nurse (which is out of habit, not hunger).
But in the end, IT DOES WORK. The reason it doesn't work is because the parent wimps out (can't handle the crying), or is not consistent with the method. Be staunch and stoic with this method! Do not give in! Or the whole sleep training goes down the toilet, because you have just proved to your daughter that crying will bring you back.
Personally, I have found that going back in longer intervals (i.e. The Modified Ferber Method) does not work. It seemed to make her crying worse, because she wondered why mama kept coming and going. So I simply said "night-night" and shut her door.
AND, vomiting is very common after crying. The baby's gag reflex is extremely sensitive compared to an adult's. So with excessive, or prolonged crying (or coughing), the gag reflex will cause them to vomit. It is harmless and again, will not traumatize the baby nor you.
So good luck...it's hard but it REALLY, REALLY PAYS OFF. Everyone will sleep peacefully, and she will learn very healthy sleep habits. Esp to put herself back to sleep. Believe me, you want to train her now, not when she is 3 years old. It gets HARDER and HARDER to train them as they grow older.
My toddler is now 2 years old, and she says "night-night" as I put her in the crib at night, and sleeps 12-14 hrs peacefully. This will go the same for you, if you are consistent and resolved with this method. Good luck.