I have always assumed, because of what is written in Scripture, that the first person to see the Risen Christ was Mary Magdalene, but there is more to the truths of the Church than Scripture, and Tradition weighs heavily.
It is in Tradition that we find the truth that the first person the Risen Christ appeared to was his mother, and as soon as I read this in the Magnificat in morning Mass, I thought, well of course, who else would he first appear to but his mother, and now the Holy Mother of us all.
“There is no mention in Scripture of her whereabouts and she is not singled out as one of the specific individuals to whom Christ made an appearance. But while the Gospel says nothing, Christian tradition has long taken it for granted that Christ appeared to his mother first. For it is logic that she who had shared most in him passion should also share in his glory. This opinion has been held by the Doctors of the Church and by the faithful at large from the earliest times.”
(Magnificat, April 2009/Volume 11. No. 2, My Spirit Rejoices page II, requires subscription)