High Elevation

My daughter is getting married at Breckenridge in Colorado next summer. It's 9,000 feet of elevation there. When I visited her recently in Boulder (5,000 ft.), I struggled. I'm quite afraid of the higher elevation we will experience for the wedding. Don't really want to pass out or vomit during the ceremony.

Anybody have any suggestions to help with this? I have seen a recommendation to take a few weeks to acclimate - but that's not really a solution.