I'm trying to socialize my pup, what signs should I be looking for to tell me that she has had enough exposure to noise, people, etc?

All pups go through many different phases of development. it can be really frustrating because it's like you don't know from day to day which pup will be coming out of the crate in the morning. Will it be the confident one, or the shy one?

With dogs or pups that show unsureness around people, I don't even go with the treat method. I teach the pup that people are neutral (like a rock or a fence post) I don't care if my pup is friendly with others, I merely want indifference. Don't push her closer to people or objects than she is comfortable, because that's what will create a long term issue.

Use her food and toy drive to keep her focused on you. I would be using marker training for EVERYTHING. I would mark (or use the clicker) for every single positive behavior she offers you and absolutely ignore anything negative and try to redirect her to something she likes to do and is successful with.

At 3 months old, she has a long way to go before she is mentally mature. Just keep working with her and try not to worry.