Best Friend is getting married to guy one month after meeting and just came out of a 2 year relationship?

Wow! She is crazy. Way too soon without knowing enough about this new guy. Can you say REBOUND! You are her good friend. Tell her you think she is rushing into this and may regret it. Then, leave it alone. It is up to her. Show her unconditional love as her friend after she's made her decision, but be sure she knows that you very much disagree.