I can understand your frustration.
What the school may do in this situation is going to be governed by the IEP. While her age does present an issue, instances like these should be covered either in a behavioral plan and / or the transitional plan, as the ability to stay on task is a life skill.
In my humble opion "just" sending her home would be an abdication of the school's duties to her and you. It would reward the behavior deprive the child the right to FAPE.
This answer contains information intended only for the use of the individual or entity named above and may be protected by attorney-client privilege or work product doctorine. However, the mere receipt of this answer, alone, is not sufficient to create an attorney-client relationship. If the reader of this is not the intended recipient or the employee or agent responsible for delivering it to the intended recipient, any dissemination, publication or copying of this answerer is strictly prohibited. The sender does not accept any responsibility for any loss, disruption or damage to your data or computer system that may occur while using data contained in, or transmitted with, this answer. Should the reader have any questions please feel free to contact Attorney Kotler at TBKotler@sbcglobal.net or 330-777-0065 Thank you and please indicate if you found this answer and / or the link(s) helpful.