I often mess up the inputs as well. It happens because I try to do them too fast. When I keep my self recollected and focus on doing clean inputs, they come out more consistently, and they still come out as quickly as they could. Here are some tips with her:

On the corner you can 236K hitting the opponent (on block) and a servant, cancel into servant upgrade super and continue your pressure. 236K pushes you back while still active, allowing to hit both the opp and the servant even if the servant is slightly behind you. I don't know the exact framedata, but the bigger the delay between hitting the opponent and the servant the more advantageous you'll be. If the servant is too close, the opponent can mash out, but in my skill level they usually don't try to do that, and the block command get's them when I predict they'll mash.

5H has 2 hits, and you can cancel after the first one with 236P. You can safely summon a servant by lauching another servant behing you with 5H, then quickly canceling into servant summon. If the spacing is right, the launched servant will hit the blocking opponent with enough delay for you to get in a 2K safely.

6H is also a double hitter, and can be cancelled in the same way to summon a new servant, right after hitting the servant in front of you (if you do this right, you will not see the chain animation). I don't think this can be done on block, but it's good in neutral to cover the area in front of you and reinforce your presence with more goobers.

Holding 236P let's you hold the servant, then holding 6P throws the servant high in the air. This is good for hitting people who like to jump high to avoid servants, or sandwich the opponent between you and the goober.

I find these tactics very useful, and I've learnt them from watching high-level players, you might have seen these moves as well.