The Queen Mother, Ramonda, arranged the ceremony, because it was a matter of court affairs.
After T'Challa ascended the throne, Princess Shuri, who should have held this authority, received the Hahnberg Research Center instead. Relying on her own scientific expertise and her reputation from the Wakandan civil war, she fulfilled former King T'Chaka's original intention in sending her to Hahnberg: to avoid political turmoil while seizing control of the research center from the other tribes. Court affairs, authority that seemed important but was actually dispensable, were handed to Queen Mother Ramonda, whose position within the royal family was awkward, according to the original plan. This was meant to ease the power struggle between the new Black Panther and his maternal family.
This was a very standard template for a court power struggle.
Court affairs had always been a position capable of bringing great wealth and influence, yet one that could not touch the true core of power. Combined with T'Chaka weakening the other nobles and clearing the way for T'Challa's ascension, any monarch who could do this much for an heir could be called wise. Yet T'Chaka surely never imagined before his death that the child of the blood relative he had personally killed would return to Wakanda for revenge, bringing a brief period of unrest to all of Wakanda.
Latveria, which had orchestrated this unrest, took advantage of the situation to seize part of Wakanda's industrial authority, exacerbating the conflict between the new king and the Queen Mother to some extent. Queen Mother Ramonda was not an isolationist. It was evident from her agreeing with her husband's idea of sending their son and daughter abroad for education that she was not as resistant as the other isolationist Wakandan nobles to cooperating with the outside world.
So when she stated