Thunder cracks and crashes in vain, and brute force proves ineffective once again.  The next obvious tactic is a direct attack, but the direction of Hisame's regard gives Procella pause.  She had hoped to divert the woman's upward gaze with her lightning, and then strike from above, but this would be too risky now: it is difficult to avoid attacks while in midair, and that sword has a very nasty feeling about it.

It presents a challenge, forcing Procella to consider her actions, to think.  She'd much rather keep using mindless destruction, but that is obviously not working.  So what does she have?  Knives are not powerful enough at long range, and too risky to bring into close range.  She has her power over charge, but lightning didn't do the job... on the other hand, that is not the only effect of charge.  

It is true that with enough of a difference between objects, a lightning strike will result, but the whole reason behind this phenomenon is attraction.  This is the basic property of charge, and the storm spirit knows it well.  Opposite charges attract each other... but are usually not powerful enough to move the objects they were in.  Increasing the force increases the attraction, but once you reach a certain point, you get electrical breakdown, and the air itself becomes a conductor for discharge, resulting in lightning.  The full explanation eludes Procella, she simply sees flashing destruction, but she is not ignorant to the pull betwixt positive and negative.

But if the object is light enough, and the charge significant but not too large... the attraction can cause simple movement.    Procella smiles.  She knows now, what she can try.

Her arm whips out, and she slashes with a knife at the leaves around her.  The uppermost ones are soaked by the rain, made heavy by the moisture, but the ones below are still relatively dry, and very light.  She cuts them away, giving each a small negative charge.  Meanwhile, Hisame still has a positive charge, since the lightning did not make it through her barrier to neutralize it.

The sensation of the building charge would be similar to the lightning attack, but instead of a blazing spark would come a sudden rush of leaves, pulled from the rivers of wind to fling themselves at Hisame.  Of course, her barrier protects her, but the leaves will not go away.  Becoming wet and adhesive as they are touched by the rain, and still attracted by charge, they will plaster themselves against the barrier, obstructing Hisame's sight as they pile on.  Procella keeps slashing, moving from branch to branch.  There are plenty of leaves to spare, and the charge needed is not nearly so great as for an electrical attack: she can sustain this, if necessary, until the shield becomes buried beneath the foliage.  

It won't get rid of the shelter, but it will delay the occupant, limit her options.  In the meantime, the storm is approaching its peak, and Procella grows stronger and stronger as it does.