Hey there,
you've gotten good advice, and I just want to reiterate two points. One, it's not the end of the world if she keeps her bottle for a few more months or even a year. When it comes to pacifiers and bottles, apparently the dental damage doesn't start until they're well on their way to 3 years old, as long as you're not letting her drink the bottle in bed as she sleeps. And I say that as someone whose kids have never really taken a bottle to begin with, so I promise, I'm not rationalizing my own issues here, I'm telling you what I believe is true. :)
Two, if she's willing to drink out of a regular cup, then go that route. I know it's messy and a pain, but honestly, it'll save you having to switch from a sippy cup to a regular cup down the line. Not only that, but once she's more comfortable with it, if you're not stressing about the bottle issue, she may be more likely to take a sippy cup since she'll be more open to lots of different ways of drinking. I say, since you're open to trying all kinds of different ways of doing this, just remember that the straw cups are apparently better dentally and developmentally, so again, if she's open (or closed) to anything, then you may as well just start there.
I believe that in all things we need to listen to our babies more. She's telling you something. So work with what she's telling you. There's plenty of room for you to get her to move forward developmentally without denying her a comfort item that she still thinks she needs. Someone said that even by 18 mos she'll have more language and more interest in other things and boy, is that true! Let it go, follow her lead a little bit, and see where you are in 6 mos. If she's still fighting you after her 2nd birthday, then you can start to worry a little. :)
Hope that helps!