I just watched the match, a few things.
Don't dsmash so much, CCing what the Fox does into dsmash is actually not that good. Drephen influenced the Sheik community too much it seems x_x. CC to grab is a lot lot better.
I think a lot of Sheik comes down to getting grab openings and then big combos off of them. Dash around the stage a bit more and use more ftilts to get grab openings instead of dash attack and dsmash. They can work but her ftilt is basically the most magical thing ever and will assist you in almost everything LOL.
Dair can be used from the ledge or occasionally when you're falling after someone hit you into the air but just don't become too predictable with it. You can actually tech chase with it on platforms as well but I question this because it's a lot easier to just waveland onto a platform and reaction tech chase imo. But if you can tech chase on a plat with dair you can lead it to other stuff which may be a lot better than getting the grab on the plat it just depends, you kinda have to become comfortable with it though.
I can never put what to do with Sheik into words very well because doing stuff with her has kinda become instinctual for me now. I would advise watching new sets of Lucien's Sheik for really good Sheik, I like Lucien's sheik A LOT and i think u could learn a lot from it.