After finishing her quest, I noticed I still have Shinwas Bracelet Shard in my inventory. How did she put together an incomplete bracelet?
Also, would that piece still be usable tomorrow? Could I give her this one without doing another quest first?
Are you sure that you finished her quest the last time that you did it? (like yesterday's quest line?) Because, as far as I know, you can keep the piece if you don't actually go back to her after doing the other NPC's quest that she sends you on, as long as you complete that person's quest you just have it as the item. (I hope that's not confusing; can't think of a better way to phrase it.) For instance, I've got one of each shard stashed away from deliberately doing just that. I used to think that they might get turned into a Genetech combination or something. [sub](i no longer think that's going to happen but...)[/sub]
As for the question if she'll accept just the shard without you also doing the quest: I just tried buying piece 1 instead of doing the quest and she totally does! :D So, you could just save your piece for tomorrow and use it instead of doing the quest when you hit that level. You may have to refresh the page and then she'll "see" it.
Hope that helps,
It's possible with all the server troubles you got a duplicate, or that you didn't complete all five quests you did for her on a previous day and so it didn't get completed by the end of the Subetan-day. It is also possible you may have purchased it accidentally from someone's shop.
If you think it might be a glitch, it might be considered an abuseable one so you should report it via Ticket in Help instead of posting in Problems and Bugs. Otherwise, I wouldn't worry.
Please file a ticket so that a staff member can look into this for you. That is always the appropriate course of action to take if you have any reason to believe that an item should have been taken but wasn't, may have duplicated, etc.