I really think she's just testing the limits, seeing what you will and won't do, what she can and can't get. You could try having one of those old fashioned egg timers, where you can see the sand going through, and she can ask for things until the sand runs out and then there are no more requests. Or you could make three 'tokens' (like a big button or a card), and each time she asks for something she has to give you a token, and when they're all ran out there is no more talking it's time to sleep. I think you just need to be firm. You know what she really needs, and what is just stalling - if she has had enough drinks in the day, gone pee before bedtime, had cuddles and a story - she really doesn't need anything else and you can say, no, no more, it's time to sleep now. Like everything, it's just about being consistent. First couple nights she will probably make a big fuss, but she'll stop bothering if she realises it doesn't get her anywhere.