What gift should I get my friend?

Maybe get her a gift certificate to a local spa?
It would be a welcome reprieve to the insanity of a wedding.

Offer to give her a bridal shower.

A gift basket left on the doorstep. Small stuff that can’t really be tampered with, like sealed bath goodies. That way you can be “secret” all you want. And if she mentions it to you, you can let it drop that it was you, either “accidentally” by saying something she hasn’t told you like, “A bath basket? How nice!” when she just says, “basket” or on purpose.