Hi M.,
Don't worry about others' timetables. I've heard of babies transitioning to sippy cups at anywhere from 6 / 8 months to 2 years old!
We tried to get my baby boy to take a sippy cup starting at about 8 - 10 months old or so and he would never take to it (even those with the soft, bottle-like "nipple" as the mouthpiece). He loved a cup with a straw, though!!
So, during meals, we would give him a cup with straw, but we still fed him his larger post- or pre-nap amounts of milk / formula from a bottle.
Since I had read that 1 year old is the target age when a baby typically transitions to a sippy cup, at every well-baby appt after 1 year old, I told our pediatrician that Connor was still drinking from a bottle for his big feedings b/c that's how we could get the most in him (and our little boy is tall and thin, so we wanted him to get as much milk and toddler formula (12 - 24 mos old formula w/ lots of vitamins) as possible. Our pediatrician seemed COMPLETELY unconcerned with the bottle thing.
And, now our little guy just turned TWO in April, and during his well-baby visit, our NEW pediatrician (we just moved to a different city) was also completely unconcerned!!
So, that should tell you that it's really not that big of a deal!!
Now, since we have a new baby coming that will be using the bottles (we are due in three weeks!), we have focused more using his sippy cups for more than just meal-time "sipping". In fact, over the past couple of months, we have gone from using the bottle for his big morning, post-afternoon nap, and before bedtime feedings to only his morning and nightime feedings, and then finally, in the past 3 weeks, to NONE AT ALL...with no problems.
Your daughter will just do it when she's ready and it's really nothing to worry about.
Hope this helps!