How do I avoid making Mary Sues?

Not to come off negative, but yeah, I can see how あなた would think she is coming off as a Mary Sue. I'm not too experienced with this, but I know that one of the ways- since あなた mentioned that she is still always positive despite- my answer to your 質問 may need to vary on whose point of view your book is in. ex: third person, first person, etc.
Okay. So, my thoughts on this, is that aside from being persistently positive, maybe have some flaws placed in such as nightmares/ bad memories, または something that most people didn't know about her (this can vary between different personality- like she's usually shy, but actually enjoys partying. The options are endless!) As far as everyone liking her, I've learned that many people enjoy what they see on the cover but hate to get too personal about someone. Maybe that's one thing, where all the other characters like her because of how または who they see her as, but not the deep thoughts of her heart.
Once again, I'm not too good at things such as this, so I really hope this helped at all.
Good luck! (:

Before あなた write a story write a characters personality then think of a couple different names that fit and pick the one あなた like best.

either way she is a proud one, so what if she is just another mary sues,,,, sshe does have a middle name. and flaws r what make us stand out to those that r worthy to see it. our spark can blind, and attact, just keep the flow, shes happy to been created , what is she helping あなた accomplish, also flaws can be totally the opposite cant it,,, good luck, thanks for the sharing?? *