First of all, kudos to you for encouraging her.
Does she play the Casio? To a pianist, it’s all about feel. To be honest, the Clavinova sounds like an upgrade, but Sweetwater have a fantastic return policy, so if you want to combine surprise with actually satisfying her desires, get her one and tell her the other is an option. If you’re not going to surprise her, then by all means, get her to try them out. Just because I say it sounds like an upgrade, doesn’t necessarily mean it is one.
https://usa.yamaha.com/products/musical_instruments/pianos/clavinova/clp-625/index.html
https://usa.yamaha.com/products/musical_instruments/pianos/arius/ydp-163/index.html