My daughter was not really into sippy cups either at that age - and not for a bit after - she just couldn't quite 'get it'. I started her with a cup with a straw (tried the plastic ones, then switched to FOOGO - stainless steel - for 2 reasons - 1st - the plastic cups sippy or straw, leaked or broke after a short time, and 2nd - wanted to get away from plastic. Foogo are expensive - but worth it when you aren't replacing the others every other month or so). She did great with a straw cup - really started to intro it at about a year - she saw it a little before that - but I didn't rely on it until around 1 yr. She adapted to that, then quickly to sippy's also and we were totally away from bottles by 18mos. My philosphy - which worked great for my dgtr was this:
No lunch bottle - went to milk in straw cup with lunch - if she drank - great - if not, no big deal. - Kept the morning, afternoon and evening bottle
Once she started getting used to the straw cup - maybe a week or so - took the morning away and gave her the straw cup w/ milk and didn't push - if she drank - great (she was still getting enough throughout the day for her)
Within a couple days after that - we were onto only an afternoon bottle and straw cup with milk for each meal. The afternoon bottle lasted a few months until I realized I should give her a snack instead of a bottle and she did well without the bottle - asked for a few months every now and then - but was really ok without it.
Once she used sippy cups (and to this day) they were for water only. I was pretty lucky - she never liked juice that much so I didn't have to worry about that or too much of it. So her sippy's were/are for water only, and her straw cups were/are for milk only. She knew what to expect and didn't get alarmed with the cup expecting one thing and getting another! I know this for the few times I thought - oh what does it matter and switch the liquid into a cup I thought she'd like better - no go. She wants to know what's coming!!!
Don't forget too - kids are all different - if she's not ready - you're in for a fight - so go at her pace too and hopefully it will all work out. As long as she's not falling asleep with it and sucking on the bottle endlessly all day/night long - she's still ok to have it.