Le'see...
Needs more dtilt. (Always needs more dtilt, lawl, its an amazing move.)
Its a great move against marth. Spacing with the tip of it will beat out pretty much everything of marth's except his dtilt and his fsmash, and you can crounch cancel -> dtilt his dtilt if you're relatively close to him. Crouch cancel -> dtilt also pretty much destroys all of shiek's approaches, and just a great overall keep away move. If they shield a dtilt, you can always just run/wavedash away before they can counterattack, or space to poke at the edge of their leg sticking out of their shield.
The DED'ing was pretty good, but you might wanna tone down on the second+ strikes. The first tap is a wide sweep, and if you space right (which you should) you can hit people's shields without being in shield grab range (which is a free dtilt/fsmash if they try and whiff their grab). Just tapping them once keeps you out of range of ther shield grab, you can just continue with the extra swipes if they don't shield, and if they shield and try to roll behind you its a free fsmash/DED combo.
More grabs are in order. Besides dthrow -> fsmash/DED, vs marth off of a fthrow you can dash a little bit -> DED if they don't DI away (roy, throw mixup, what???). Fthrow -> running forward pivot fsmash can combo if they DI poorly, and can tip sometimes for a slight bit more knockback if they don't DI at all.
Shiek falls fast, so on top of maybe a dthrow -> fsmash, fthrow is a free techchase.
Despite popular belief, down air is a great move. Its got a little more lag on it, but its got a huge sweep, and combos very nicely into fsmashes at a wide variety of percent. Use it.
Flare blade sucks at edgeguard against pretty much everyone except space animals and falcon/ganon. Marth can hit you out of it, and shiek's sweetspotting won't get hit by a flare blade. You're better off getting to the edge as fast as you can to set up for a roll/ledge hop -> fsmash. A tip dtilt at the edge can also set up nicely for a full jump flare blade, which can lead to a kill (plus, if the dtilt misses you can always just wavedash backwards and proceed to make their job of getting up from the edge to the stage a nightmare).
Constructive criticism aside, not too bad. The DED spacing was good, and the fsmashes were nicely timed. Overall speed was pretty good, too. You just need to work some on being safe while still approaching quickly, and capitalizing on the hits you do get in