I have known a
Mandy who was short for Mandolin. I like a good instrumental name occasionally. I don't think you're overthinking it I think you're giving it an appropriate amount of thought.
Mandy by itself is okay too. Don't use
Amanda if you don't love it.
Here is a search of "mand" names I did for you. Be sure to look at the user submitted ones too.
https://www.behindthename.com/names/gender/feminine/substring/mand
Please rate my "Names I would Use" list & "Backup Favorites" list. Feel free to rate some of my other lists too if you have the time.
https://www.behindthename.com/pnl/223226/138473