Catteleya Hybrid dropping green leaves, is this normal?

[Mira-Claude]

I too would unpot the cattleya to ascertain the state of the roots. They look a little dehydrated.
A botanist told me that the best way to make sure the roots are healthy is to soak the plant for fifteen minutes and then lightly press on them. If they are firm, what ever the color, they are fine. If they are mushy it is best to cut them off. If you lightly pull on them and the cover of the roots comes easily it's fine, just keep pulling but leave the little cord inside be. I am uncertain about the fact, but some people says it can still absorb some liquid.
As for potting media, you would be surprised what you can find in a petshop. There is mounts, coco husk chunks, sometimes bark too.
In this case I would go with mounting as cattleyas do like to dry out. Just make sure to water her once a day and spray her early evening if it gets really dry and hot.
Good luck!