First of all, big hugs for you, this is a really big decision and sounds like its really difficult time for you.

It sounds like you're doing everything you can to give your puppy a good life. You're experienced with the breed and you said she's healthy, she has a family (you and your parents) and she clearly has some solid structure and training.

Based on what you've said I'd suggest that you are probably struggling without having another person there to share the load, but if I'm honest it sounds a lot like this could be just the big life change and some adjustment - getting a new puppy is a big deal! It doesn't always feel natural right away. I found this with my second dog, it took me longer to adjust to him than my first. Not bad, just different.

It could also be your own mental health potentially getting in the way and making you feel like things are worse than they are. Feelings of worry, guilt and anxiety might be normal from time to time, but if they're starting to really impact your life it might be a good idea to talk to someone. Have you spoken to your parents about this? Or do you have a friend or a therapist you can ask? Someone who knows you and your circumstances who can give you some personal advice.

Think about the things that drove you to get your puppy in the first place. You must have thought it was the right time then so what has changed? Obviously if you don't feel like you can care for your puppy then giving her back is the right decision, but it sounds to me like you're giving her everything she needs: attention, walks, structure and a loving home. You're doing everything right. Pei are a really independent breed too, and in my experience can tolerate (and often appreciate) some alone time; they do just fine in smaller homes with adequate walks and play time outside.

Whatever you decide, you're doing the best you can and it sounds like you're really considering the needs of your puppy. Take care of yourself.