Laura started from her chair, Flung her arms up in the air, Clutch'd her hair: "Lizzie, Lizzie, have you tasted For my sake the fruit forbidden? Must your light like mine be hidden, Your young life like mine be wasted, Undone in mine undoing, And ruin'd in my ruin, Thirsty, canker'd, goblin-ridden?" -
Laura sees her sister and jumps up.
She's afraid that Lizzie has gone and eaten the goblin fruits, too, so she throws her hands in the air in despair.
Laura is terrified that Lizzie has eaten the "fruit forbidden," and that she'll waste away, too.
She doesn't want to drag Lizzie down with her.
She clung about her sister, Kiss'd and kiss'd and kiss'd her: Tears once again Refresh'd her shrunken eyes, Dropping like rain After long sultry drouth; Shaking with aguish fear, and pain, She kiss'd and kiss'd her with a hungry mouth.
Laura hugs Lizzie, and kisses her again and again.
Of course, since Lizzie is drenched in goblin fruit juice, Laura gets some in her mouth.
Laura hasn't been able to cry for days, but upon seeing the sacrifice her sister was willing to make for her, she starts to cry again.
Crying "refreshe[s]" her.
Laura is actually "shaking" with a combination of "aguish," or feverish, "fear and pain."
She just can't stop kissing her heroic sister. Of course, she's kissing her with a "hungry mouth," so there seems to be an element of greed here, as well as gratitude and affection.