I think my wife has some kind of cognitive disability
What makes you think your wife has a cognitive disability?
She thinks I don't love her when I show her all the time I do.
It's likely that your wife is dealing with some insecurities. It may be beneficial for you both to attend couples therapy together.
I can afford a vacation.
A vacation won't solve the problem your facing. Attending therapy together will help you to understand if you are loving her the way she wants to be loved. Everyone speaks a different love language and it's possible that you are not speaking hers.