it's different with all babies.... my first was babbling from day one, started using words like mama, dada, baba, etc, around 7 months, knew what they meant by 9 months (plus had a whole string of other words), and by a year old was talking in sentences that i could understand (not that many other people could understand her, but her dad and her gma and i always could).....
my second hardly made a sound (except to scream her head off) until she was much older! she just didn't talk.... it worried me for a bit, but then one day, around 2-ish, maybe(?), she just started talking.... and now she won't shut up!
and now my third is 9 months old and she is a babbler, but not quite as much as my first, and not quite as clearly either. but she does have some very distinct words for certain things....
anyway..... that's my kids. all three are very different in their "milestones" as are all kids. don't stress, she'll start talking like crazy one day and you'll look back on these more quiet days with fierce longing!!!
and hey, take advantage of her babyhood while you can! it goes by so FAST!!!! don't get impatient for her to get too big too fast, because before you know it, she'll be getting ready to start kindergarten and you'll be wondering what the heck happened???!!!!??!?!!! (my first starts kindergarten this year and it's crazy how fast it's gone!!!)