The boring part of speedrunning is doing the same conversations over and over again, to find the fastest way through them.
Nancy starts the game by talking to Jane. Jane says, "I bet my bloomers you're Nancy Drew." If Nancy says, "That's right. Are you Emily's guardian?", Jane says, "You got it. I'm Jane Willoughby." If Nancy says, "Emily told me your name. It's...", Jane says, "I'm Jane Willoughby." It's about a second faster to pick the second option, the one where Jane says less.
Then Jane and Nancy talk about pies and Nancy's father. Jane says Emily didn't say anything about Nancy's arrival. Nancy can ask, "Is it okay that I'm here?" or "She didn't?". Jane's response is the same either way. So again, it's about a second faster to pick the second option.
The third choice is trickier. If Nancy says, "Is she all right?", Jane responds with, "Well, now, that's hard to say. She misses her mom...". If Nancy says, "Maybe she's just...you know, still thinking about her mom.", Jane responds with "She misses her mom...". That is, Nancy's shorter option is paired with Jane's longer response, while Nancy's longer option is paired with Jane's shorter response. It's about 0.4 seconds faster to pick the first option, where Nancy says, "Is she all right?".
With the fourth choice, Nancy can ask about Emily's father, or say "It was nice of you to say yes". It's about three seconds faster to say, "It was nice of you to say yes," because otherwise, Jane talks about Mr. Crandall for three seconds.
With the fifth and final choice, Jane's response is the same either way. She ends the conversation and tells Nancy to go upstairs. It's about 1.5 seconds faster to pick the second conversation option, "Help her do what?".
So overall in this conversation, there are two places where it doesn't matter which option you pick, because Jane has the exact same response either way. There are three places where Jane has the same response either way, but she says an extra sentence if you pick a particular option, so you have to pick the option that avoids the extra sentence.
Does that make sense? The fastest way through the conversation is to avoid having Jane say extra sentences. If you've got a place where she doesn't say extra sentences, then pick the option which is shorter.