I never go on to sippy cupos as i find it's just another thing to try to teach bubs & so from about 6mths (when they start solids etc) I offer a cup (I have a really old mag Mag one from Maddy & a new one) with straws, Indah has sucked easily from a straw from 6mths..
Maybe try a cup with a straw?? Or start teaching her how to go straight to holding a cip.. I do this in the bath.. Letting Indah have a cup in the bath they cant get anymore wet can they & she ALWAYS drinks her own bath water anyways so it's easy, she now drinks from a cup in the bath all the time & now out of the bath as well..