I really love the Catelina suggestion - so similar to [name_f]Caterina[/name_f], but should resolve the issue of the Ts and Rs with the last name.
Also like the [name_f]Karina[/name_f]/[name_f]Corrina[/name_f]/[name_f]Corrine[/name_f] suggestion (tons of NN possibilities like [name_u]Kari[/name_u], [name_u]Corey[/name_u], [name_f]Coco[/name_f], [name_f]Nina[/name_f], etc. that would allow her to stand apart from the [name_f]Kathryn[/name_f]/[name_f]Katie[/name_f]/[name_f]Kate[/name_f] names but still honor your grandmother).
Definitely worth exploring the suggestion to run with the “[name_u]Kay[/name_u]” sounds too.
[name_f]Cadence[/name_f], [name_f]Calista[/name_f], [name_f]Callie[/name_f], [name_u]Calypso[/name_u], [name_f]Camille[/name_f]/[name_f]Camilla[/name_f], [name_f]Calliope[/name_f], [name_f]Calixta[/name_f], [name_u]Cameron[/name_u], [name_f]Capri[/name_f], [name_f]Carissa[/name_f], [name_u]Carlin[/name_u], [name_f]Karla[/name_f], [name_u]Carmen[/name_u], [name_u]Carter[/name_u], [name_f]Cassia[/name_f], [name_f]Cassie[/name_f], [name_u]Cassidy[/name_u], [name_f]Celeste[/name_f], [name_f]Celestina[/name_f], [name_f]Chloe[/name_f], [name_f]Clarissa[/name_f], [name_f]Cleo[/name_f], [name_f]Cressida[/name_f], [name_f]Kaia[/name_f], [name_f]Kara[/name_f], [name_f]Katia[/name_f]/[name_f]Katja[/name_f]/[name_f]Katya[/name_f], [name_f]Keira[/name_f], [name_f]Kyla[/name_f], [name_f]Kyra[/name_f], [name_f]Charlene[/name_f], [name_f]Charlotte[/name_f], [name_f]Carlotta[/name_f], [name_f]Caitriona[/name_f], [name_f]Catriona[/name_f], [name_f]Cambria[/name_f], [name_u]Kit[/name_u], Kitanna.