"I'll go with you!".

He tells her what she must do and she launches herself at him and tries to put as much as she can into a hug.

During the hug, her mind flashes back to her in a dead sprint to hug him after she was unpetrified; her holding onto his waist as tight as she could before rescuing Sirius; her jumping up and down in excitement that he made it past the dragon; her sobbing on his shoulder on that staircase after Ron kissed Lavender.

When the hug was broken, she stepped back and took a good look at him, realizing it may be her last, and that when he came back, it would be over and they could finally settle down, and be together until the very end.