That sentence is incorrect. Maybe you were trying to say:
هي ليست واقفة
This is if you meant "She isn't standing".
لا is used before infinitive verbs for instructions or imperative verbs, it's called:
لا الناهية
eg:
Don't stand here. لا تقف هنا
Don't eat now. لا تأكل الآن
لا has more other usages