Hello! MizukoWaterchild I have been trying to comment on your chapters, but it Wattpad won't let me. This normally happens whenever Wattpad just updates, but I am here for the symbol of the book!
So, straight off the bat, I would recommend a siren. At least, normally, but I wanted to go a bit deeper than that.
A dragonfly for courage, hardship, happiness (found in her friends and new family), and strength (which Shizukana shows throughout the entire story)
A pine tree for the reasons above. Tbh, Kakashi, Hikaru, Kiba, Shikamaru, Ren, and many many more are like Shizukana's pine tree!
Water, because let's be honest here, she's he child of the water. (Ayeeeee reference to your username)
Of course the chains for her being chained to 'destiny.' Personally, I find her last was her destiny because without it, she would've never met everyone she has.
These are some symbols that are self explanatory. She protects her loved ones more than herself though.
But yeah! Those are just some ideas. Also, thank you for updating and making a sequel! Keep on writing! You're a very strong writer and here's a tip when you are editing: rewrite the entire chapter word by word, it will help you find more mistakes and don't edit until you are finished with the book.
Have fun and keep writing!