I agree with the previous response: it's never too early to start sippy cups (my son fell in love with them at 6 months).
My son lost interest in his bottles early. Believe me, it's normal that your daughter is playing with the cup. Sometimes, they become "drumsticks" or great noisemakers. My son misplaces about 3 of his cups a day because he likes to "see them fly" or "see how far they fall." LOL :)
Transition her to the cup by giving her the formula in her cup in place of maybe one to two bottles AND give it to her when she eats. You can put juice or water in it at that point.
Hopefully, she'll get the idea that the cup is for her to drink out of.