Most girls do play multiple sports, however, focus on lacrosse when there is a conflict. Reality is that most club team install their offenses in the fall and if you miss too many fall practices you will be behind.
Biggest fall tourneys are
Lax For The Cure (1-day) Fall Draw (1-day) Chespeake Invite Mid Atlantic Fall Live Love Lax
For high school aged girls, IWLCA in Dallas is a major recruiting event.