You should teach English sounds. Let Grandma teach Thai sounds. Don't worry.
What does a ________ (pig/elephant/duck/rooster/frog/dog/cat) say?
A _______ says ________.
Your daughter will understand that "duck" is an English word so there is a different sound for it than the Thai word. Don't worry. It is the same as everything else. One word in Thai and a different word in English.