Many babies are not fully developed in this area until they are 12-15 months old. The problem with acid reflux is that it can get worse over time....meaning she may have been happy thus far, but the lining of her esophagus and throat may have been exposed to the excess acid backing up for quite some time, and it may finally getting to be painful for her due to the burning of the back of the throat. If this is the case, she will most likely need to get put on acid reflux medicine to help with this until she is a little older (when her body has had time to completely develop).
I would call your doctor's office. Explain that you recently had her 6 month well-check (presumably?), but you forgot to mention her excess spitting up, etc. Ask if they will prescribe a medicine for your daughter without you having to come in (chances are you'll be back in for her 9 mo well-check, and they can see how the progress is at that point).
Both of my children were GERD babies. My son was on prevacid for probably 12-15 months of age. My daughter started out on Zantac, and then we ended up switching her to prevacid after a couple of months, because the Zantac wasn't working for her. She is now 14 months old and has been off of all acid reflux medicines for 2 months.
**Also, keep in mind that this medicine is not going to stop the spitting up. It should help quite a bit, but your daughter will still spit up some. The difference is that the amount of painful acid in the spit up will not be quite as potent as before.