Uh, yeah! Let the bride or groom know that you’re wobbly in heels and ask if they can pick you out a pair to wear while walking down the aisle and standing during the ceremony.
Offer to buy the heels as well (so you’ll be buying two pairs) to wear during the photos so your bride or groom can still get the look they’re going for without watching you topple their entire bridal party during the ceremony.
If they won’t relent, practice walking and standing in heels leading up to the big day and then slowly wean that friendship post-wedding. What kind of petty friend insists you wear heels when you can’t? You don’t need that negativity in your life.