Look, if it is bugging you that much, just be honest and say "NO. I'm not down with that because I'm worried it would weird out the friendship I have with her. I'm already worried you are too dependent on me."
Or if you are willing to entertain a discussion (that means discuss, not automatically say "yes!" could still be "no!") say THAT. "I'm not crazy about it. I am worried it would weird out the friendship I have with her. You picking someone so close to me worries me that you are too dependent on me. You can see if she's even interested. If not, it doesn't matter. If yes, then I'm willing to discuss it. But it could mean we end if you guys decide to date and I'm still weird feeling. I would try to remain friends if so."
Just grab the bull by the horns.
You have the responsibility to know and state your wants, needs, and limits.