Just to come in as we had this exact same predicament for DD's christening. my DD was much younger than yours is now but roughly on the same routine. We opted for an early CN, just plopped her in bed whilst everyone was getting ready. Yes, she did an UT 40mins nap, but we kept her in bed for as long as possible (turned out only an extra 15mins), then got her up and dressed and off to church.
We had a family BBQ when we got back so lots of stimulation. But yk what, she handled it brilliantly. I did think she was getting a little tired around 3pm so tried for a nap. She refused it but at least she had 30 mins down time (she wasn't crying or anything). Got her up again and she happily played until everyone left around 6pm. Had the quickest bath and bottle and into bed by 6.25/30pm. For the first time ever she was asleep in 5mins. All I really wanted to say is that I prepared for the absolute worst and she handled it so amazingly, I was so proud. So I'm sure it'll be the same for you hun xx