No, the first clue of Lavender's feeling for Ron is her inappropriately loud giggle at a moderately amusing comment of Ron's after the Welcoming Feast in sixth year. She continues to drop hints of her interest in him. Ron is flattered by the attention. They start dating after Ron, believing himself to be under the influence of Felix Felicis, helps Gryffindor win the first Quidditch match of the year. Ron loses interest in Lavender after his brush with death when he is poisoned on his 17th birthday. Lavender ultimately breaks it off after seeing Ron emerge from the boy's dormitories with Hermione and assumes the worst. (Harry was really there as well but under the invisibility cloak.) Also, it is worth noting that Lavender went to the Yule Ball with Seamus Finnegan in Goblet of Fire and was quite giggly about it.