There are many things to learn in past and present perfect. That said, actually, the question is broad. But I'll try to restrict my answer that precisely addresses your concern and you might find it helpful.
You said - She has drunk milk refers to past perfect - wrong!
And you want to learn the difference between past/present perfect.
The gist of those tenses lie in the structure of the sentence and its context.
In most of the cases, we use the present perfect while referring something that started in the past but its effects are still in the present.
She has lived in this apartment all her life
The sentence structure is
has/have + past participle
Now, when we use the past perfect, we refer thing that are already happened in the past. And we may also want to point something before that time.
The structure is
had + past participle
She had lived in this apartment all her life - she's dead now!
I found the best reference of British Council to learn the past perfect. Check out the nuance of past simple and past perfect on the page.
So, do you now see how do you differentiate these usages?
Getting back to your concern - She has drunk milk - you said it past perfect. Do you realize now? Check the sentence structure... :)