As nearly as I can express it, she seemed to "wiggle" a little, although that isn't the word.

She seemed to hang out a sign "Oh, look--look at me!"-- and that doesn't quite describe it, either.
Just as Master McAllister reached them, raising his hat and bowing to Mary and her friend--Helen's eyes and Helen's smile unconsciously lingered on him for a second or two until, apparently recollecting that she was looking at another, she lowered her glance and peeped at him through her eyelashes instead.
Mary meanwhile was calmly continuing her conversation, never even suspecting the comedy which was going on by her side, but when Helen shot a glance over her shoulder and whispered with satisfaction "He turned to look!" even Mary began to have some slight idea of what was going on.
"Helen," she demurred, "you should never turn around to look at a young man." "Why not ?" laughed Helen, her arm going around her cousin's waist.

And speaking in the voice of one who has just achieved a triumph, she added, "They're all such fo-oo-ools!" Mary thought that over.
Helen's correspondents continued active, and as each letter arrived she read parts of it to her cousin.

She was a mimic, and two of the letters she read in character one afternoon when Mary was changing her dress for dinner.
"Oh, Helen, you shouldn't," said Mary, laughing in spite of herself and feeling ashamed of it the same moment.

"I think it's awful to make fun of people who write you like that." "Pooh!" laughed Helen.