TECHNICALLY, Hitnrun is correct in his take on the OHSAA Return to Play Protocol after sustaining a concussion. However, there is not an OHSAA "violation" or "consequence" for doing so... It could POTENTIALLY be MUCH MORE serious than that. It is actually a state law and guided by NFHS playing rules... meaning, if something would have happened to her while she was in the game (notwithstanding intent and caution) all parties would be subject to litigation...I missed this earlier but what a ridiculous take... so no senior should get to enjoy one small moment of what otherwise typically was a terrible end to their senior season and possibly career because they have a condition or injury that doesn't allow them on the floor? When these situations are set-up, there are literally no other players near them on the floor and all precautions are taken to ensure the health of the athlete. This is commonly done for kids and it is a mark of great character and great sportsmanship, not this twisted view that you took.
This is entirely different than a typical "injury" that you refer to like an athlete rehabbing from an ACL tear or other major physical injury / surgery. Head injuries, particularly concussions, are significantly different as indicated by a specific state law and guidelines set forth by the NFHS and OHSAA to return to play.
BUT I do understand the point you are making. The athlete and parents are free to allow this to happen HOWEVER... this is a VERY RISKY move for the school unless they fulfilled the following or have no problem paying court costs if they were to be sued which in this particular situation, I HIGHLY doubt anyone makes a big deal about it. You just never know...
OHSAA Concussion Protocol
...the coach or contest officials shall not permit the student to return to practice or competition until both of the following conditions are satisfied:
1) The student’s condition is assessed by either of the following:
a. A physician, who is a person authorized under Chapter 4731 of the Ohio Revised Code (OCR) to practice medicine and surgery or osteopathic medicine or surgery (M.D. or D.O.)
b. Any other licensed health care provider that the school district board of education or other governing authority of a chartered or non-chartered nonpublic school, authorizes to assess the student who has been removed from practice or competition.
2) The student receives written authorization that it is safe for the student to return to practice or competition from a physician or other licensed health care provider authorized to grant the clearance.