Some kids just take a little longer. My daughter took what seemed like forever to hold her bottle by herself, and wasn't totally switched over to all sippy cups until she was 13 or 14 months, I think. I started replacing one bottle a day with a sippy cup when she was about 10 months old, and just gradually increased the number of sippy cups until the bottles were gone(started with lunch, then dinner, then breakfast, and left bedtime for last). I tried a bunch of different sippy cups with her. She liked the Nuby ones with the soft top the best- they even have one with handles on it and a cover for travel. The only problem I've had with them is that she likes to chew on them, and I haven't found a place that sells the insert. At about $1.70 per cup, they aren't expensive, though. The take and toss cups are actually really great as well, although I never bring them when we go out. They are really cheap (5 or 6 for about $2.50), are dishwasher safe, they don't have a valve, and the lids stay on about 99% of the time (have to drop them on the floor at just the right angle to get the lid to come off). I really don't like the Playtex ones with the handles. They really aren't good for teaching because you have to suck so incredibly hard to get any liquid out-it's crazy! If you take the valves out of them then the liquid pours all over the place and the child chokes. I ended up cutting a bigger slit in the valves so it was a happy medium. The Walmart generic brand (Parent's Choice?) leaked so bad that I took it right back after the first use. I'd recommend not using the ones with the straws until she gets totally off the bottle and has mastered the sippy cup. It is a totally different skill to learn, and it might confuse her. Besides, cleaning those straws are a pain, and the dishwasher seems to "eat" them, because they disappear. Another one I love to use now is the Playtex Sipster. They have a valve, but they aren't difficult for my daughter to drink out of, are leakproof, not as expensive as some of the other ones, and it's easy to get a good seal when you put the lid on. They don't have a cover for travel, though. Some of the Nuby's come with covers, so they are great to bring when you go out.
As far as how much milk/formula to give her, at my daughter's one year appointment our doctor told us the minimum was 24 ounces until she was 2 years old. I know my daughter was drinking 32 ounces a day until she was about 11 months old. One thing to keep in mind is that the solid food she is eating is going to replace some of the "food" in the bottles (milk/formula). That is why she will start to drink less formula. When she turns one you can switch her to whole milk- happy day- much cheaper!! =)
Don't stress too much about it- she'll catch on when she is ready. One thing I realized with my daughter is that she didn't want to hold the cup for some reason. If I held it for her long enough to get a few sips, then she would do better and start to hold it herself.
Good luck.