Scizor
-X-Scissor
-Iron Head
-Aerial Ace/Night Slash
-Agility/Aerial Ace/Night Slash
Yeah, I've never noticed how Scizor's Speed stat is so low. But this moveset should serve her well.
X-Scissor and Iron Head, both are powerful Physical moves and will recieve STAB.
Aerial Ace or Night Slash. Either is fine, but I'm more biased towards Aerial Ace for some reason. Your choice though.
And I guess there's a reason why Scizor can learn Agility.
If your speed problem is bugging you too much then I suggest Agility. Scizor has nice Defense and decent Special Defense, and so taking a turn or two to use Agility may be attractive.
If you're not a fan of moves like Agility, then just go with what you didn't chose for the third move. Like if you chose Aerial Ace as the third but don't want Agility as the fourth then just stick Night Slash on there.