Who are you to control whom she has become?
If she becomes materialistic, there is nothing you can do to stop
her. It is her body, her own characteristics, so she is the only
one who can have control over it...
And wearing those earrings don't necessarily mean she has become
materialistic/attention-seeking. She might just want to try out
something new instead of wearing the boring old pair of stud
earrings all the time. Heck, even I have a 5cm dangling earrings,
with a big red bead dangling at the end of it to boot. But I don't
consider myself materialistic at all, and my friends can testify to
that.