Are you breastfeeding or formula feeding? Are you giving her cows or goats milk?
I don't know if you are or not, and for the sake on convenience, no baby is allowed to have cows milk before they are about a year old because they cannot digest the protein in it.
If you are breastfeeding, burp her between sides to minimize the milk coming up with the gas bubbles. If you are formula feeding, you can burp her every few ounces. Make sure you don't give it to her with lots of bubbles in it, because that's sure to make it come right back up.
A little spit up is normal. If you are formula feeding and she's throwing up the whole thing or a great amount of it, is not gaining much weight, seems hungry all the time, then she is spitting up too much, and you will have to talk to your pediatrician about switching formulas.
Try a slow flow nipple. I have found that if it comes out too fast they ingest it too fast, which they cannot handle and spit right back up. If not, it may be the formula, let the doctor know about it.