I would be tempted to go with another variation entirely, like your [name_f]Katharina[/name_f] or the Italian [name_f]Caterina[/name_f] or my favourite the Spanish [name_f]Catalina[/name_f].
I like the idea of [name_f]Kathleen[/name_f] I think its a beauitful name and a diminutive of [name_f]Katherine[/name_f]. Or [name_f]Catharyn[/name_f] looks pretty! or [name_f]Cathryn[/name_f].
While you’re right that [name_f]Catharyn[/name_f] technically fits the bill the best, I would vastly prefer [name_f]Katharine[/name_f] - it looks very dramatic and sophisticated to me, plus it technically honours the two "[name_f]Katherine[/name_f]"s who are in your life (no disrespect to the Duchess of Cambridge but it doesn’t sound like you know her personally?).
I like the idea of using [name_f]Katharina[/name_f] - it’s a nod to all the ‘Katherines’ but it has your own spin on it, so it doesn’t feel like it’s privileging any one over the others
I would just go with whichever spelling of [name_f]Katherine[/name_f] you like best other than [name_f]Kathryn[/name_f], [name_f]Catharine[/name_f] and [name_f]Catherine[/name_f], since I think if you choose one of those spellings it takes away a bit from the idea of honouring all three of them. But I think [name_f]Cathryn[/name_f] or [name_f]Katharine[/name_f] or [name_f]Katherine[/name_f] or [name_f]Catharyn[/name_f] or any of the other variations ([name_f]Katarina[/name_f], [name_f]Kathleen[/name_f] etc) work equally as well as an honour name for those three. My personal favourite is [name_f]Katharine[/name_f], followed by [name_f]Katherine[/name_f].
[name_f]Do[/name_f] you like any of the nicknames? [name_f]Kate[/name_f]/[name_f]Cait[/name_f], [name_u]Kit[/name_u], [name_f]Kitty[/name_f], Kath, [name_f]Kat[/name_f]/[name_f]Cat[/name_f]?
I really like [name_f]Katharine[/name_f] for all three "[name_f]Katherine[/name_f]"s. [name_f]Catharyn[/name_f] works well, too, but [name_f]Katharine[/name_f] is my favorite.
I think using [name_f]Katharina[/name_f] would be perfect for you as it still encompasses all three namesake variations quite well, with an added -a to make it her own, and is a name you adore.
Seeing as all three names are different variations themselves, I’d go with another variation - like [name_f]Katharine[/name_f]. I know that there are a dozen different ways to spell it, but [name_f]Catharyn[/name_f] is just a bit too smooshed together, in my opinion. Especially when you have a classic option like [name_f]Katharine[/name_f]. [name_m]Even[/name_m] in your signature you list that one of your naming pet peeves is “unconventional” spellings, which [name_f]Catharyn[/name_f] would fall under.
Thanks, everyone! I know [name_f]Catharyn[/name_f] kinda looks weird… I guess I just was considering it because my two favorite spellings of the name are [name_f]Kathryn[/name_f] and [name_f]Catharine[/name_f]… I love the nicknames [name_f]Kitty[/name_f] and [name_u]Kit[/name_u] and [name_f]Katja[/name_f], too…