I doubt if a piece that small is going to cause any serious problems.
My experience is that when cats eat something indigestible, they
either barf it up immediately, or it eventually passes out the other
end.  Things that might cause problems are stuff like string or
Christmas tree tinsel that can get tangled up in the intestines.

BTW, when I was a kid, we had a cat who had a fetish for eating
styrofoam.  It started when she first began begging to be fed popcorn
when we were munching on it ourselves -- I think she liked the grease
and salt.  But apparently, she couldn't tell the difference between
real popcorn and styrofoam packing "popcorn".  :-P  Of course we didn't
feed her styrofoam on purpose, but she always wanted to investigate if
we got a package.  Anyway, she lived to a ripe old age and never
seemed to suffer from her odd snacking habits.

-Sandra the cynic

Call your vet and ask them?  They can tell you if this will pass or if she
needs to be seen.

Celeste

You need to call your vet    the product can swell up and is not easily
passed.
It can take several days before an real symptoms show up after ingesting
Styrofoam