In the dialogue,
Q: How did you like the movie?
A1: It was pretty "good".
A2: It was "pretty" good.

I read that the meaning changes as she stresses differently.
A1: She liked it
A2: She didn't like it much.

Is that right?

Hi Leo! Great question. In general, yes that would be true. But in this case there is a bit more nuance involved because it would also probably require more subtle body language or tone to derive the meaning. In the first case, the person would probably say it with an enthusiastic tone and a smile saying, "It was pretty good!". In the second case, if they thought the movie was just okay, they probably would put more emphasis on the "pretty" rather than the "good", but they would also maybe add a shrug and say, "It was pretty good, I guess", or something like that for more clarity. In the second case, most likely just emphasizing the "pretty" by itself without those other nonverbal and verbal clues would be too ambiguous to interprate the meaning.