Toilet training

Hi everyone 

I'm new here,  my 3 yr old girl was diagnosed with ASD 2 weeks ago,  she's still in pull ups, I really want to start toilet training come the spring/ summer 

Does anyone have any advice, tips she doesn't like being sat in poo (sometimes) but doesn't really acknowledge the wees.

Because she's a big girl (tall and chunky) the dr recommended going straight to the toilet and forget the potty.

She does ask to sit on the big girl toilet sometimes which i do our her on and praise her for being such a big girl.

The Dr thinks I should keep her in pull ups and try and get her into a toilet routine like

Sit on the toilet as soon as she's awake,  then on the toilet 20 minutes after food/breakfast, again after lunch repeat after dinner and before bed, just to get her into a routine, does this sound right?? Does anyone have any other tips?

Last year when I tried i took her out of pull ups and she would sit on the potty and but refused to do anything on it, even though I ran water, often went for a wee myself she did nothing and with 20 minutes of being away from the potty she would do it in her knickers and clothes and wasn't bothered at all,  happy to sit in poo. 

She sometimes says she's done a poo but not a wee

I'm desperate and feel this would give her such a big confidence boost to reach that milestone. 

TIA