Her Fair works relatively well as an air-to-air move, as in it's pretty good in those situations where you and your opponent jump at each other at the same time and you gotta throw something out quickly. Granted, in these situations you're probably better off jumping with your back facing the opponent for Bair since that has a much higher reward, but Fair might just be more reliable in these kinds of situations.
Hitting the ball with the back hit spike of Fair after doing a Header Cancel sends the ball super slow at a downwards angle, allowing you some close range pressure while onstage or some interesting edgeguard setups for recovering opponents.
Also, if your timing is true, run off stage > Fair is excellent at snagging the back hit spike on characters who use horizontal 'mobility moves' to grab the edge from low. The two biggest examples here are Diddy and Fox.
.
.
.
As far as Dtilt, there aren't TOO many uses for it. From what I can tell, it IS her longest range tilt horizontally, and it has some situational anti-air capabilities so it's not the worst thing to throw out in neutral. The biggest use I've seen for it, though, is the follow up from burying someone with Jab. It's a relatively fast move that gets a nice, hearty 12 damage, and you don't have to worry about missing from the low height of the opponent since it's a low attack itself to begin with.
.
.
.
Utilt is kind of frumpy, because it has rather low damage, a ton of ending lag, and you need some good timing to actually hit with it, but it is an excellent anti-air move, when used out of a crouch. I've had this thing beat out Sheik's Fair, so you know that's a pretty nice perk all by itself.