My daughter had mastered a sippy cup and a straw well before a year...so I know it is possible.
One thing I noticed with "no spill" sippy cups and straw cups was that the valve inside made it REALLY hard to get fluid out of the cup and up the straw--really just glorified bottle. I found that that the "take and toss" type cups were a fast road to success. I used a hot paperclip to enlarge the hole on the sippy cups (though I found one or two with free-flowing holes) and the straws have no valve. My daughter is three now and we've been using the same cups for at least two years now.
Granted, the lid just snaps on...so if she really chucks it across the room you are going to have a spill.
When she was learning, I would just demonstrate the sucking motion without a straw...they are good at mimicking and make the association in no time at all. Exaggerate the motion a bit when you are drinking from a straw yourself...it only takes success a time or two before they get it at this age.
I still pull all the no spill valves out of cups that we have. I wanted her to learn that she can't just set a cup down anywhere...she needs to keep things upright and I think it has helped with open cups as well.
Good luck.