I say, just let her have the collage at your bridal showe if she already made it. It's not that major.
As for the wedding, mothers are SO pushy!!! Mine seriously is insane about mine and is always pushing her ideas on me and gets mad when I reject them. BUT she's not paying for my wedding. We are. If she was paying for it, I'd prob let her do whatever she wanted (with my input, of course). But since she's not, I just say, hello, it's my wedding and I"m funding it, so no. LOL.
Wait, I want to edit this... If she were paying. I would let her do a LOT of what she wanted but not everything. LOL. Just tell her straight up what you want. Mothers are really sensitive so just try to talk to her. I wish I could take my own advice. Mine is driving me nuts! You are not alone!