I had to think about this for a while, but I think I prefer the [name_f]Cecelia[/name_f] spelling.
I couldn’t tell you why, though! 
Thanks everyone! I’m pretty sure we are going to go with [name_f]Cecelia[/name_f]. I just like it more.
If [name_f]Cecelia[/name_f] was the more common spelling of the name here in the U.S. initially, then I feel like it is more traditional. Somewhere along the line [name_f]Cecilia[/name_f] took over, so now that spelling feels more correct/traditional.
Visually, I think [name_f]Cecilia[/name_f] is more appealing.
I prefer the [name_f]Cecilia[/name_f] spelling. The only girl I’ve ever known with the name spells it this way (she’s Mexican). [name_f]Cecelia[/name_f] just looks wrong to me.
I pronounce both spellings the same way - suh-[name_m]SEEL[/name_m]-yah.