How to deal with an overly sensitive child?

Lately my daughter, who just recently turned 6 has been EXTREMELY sensitive about some things lately. Its also irrational and silly things, like this week we went to the dentist for a check up and got new toothbrushes, so that night when we brushed our teeth I threw away the old one as we have a new one and it definitely needed replacing. She had a total meltdown about throwing away this toothbrush. When she has a meltdown like this I try and talk to her, have her talk to me, have her go to a "happy place". Nothing works, or sometimes makes her more hysterical. It has just gotten extremely frustrating, and it is a recent thing. So I don't know if its a phase or what, but does anyone have any ideas and what I can do to calm her down or how to not make things a total meltdown??