I am certain that the reason why her memory stops before the time she met you is because
あの子の記憶が
あなたと出会う前で
止まったのは
Besides,Just maybe, something might make her remember everything that has happend until now.Thank you, Yukari.that child must be feeling that meeting you was the best thing that has ever happend to her.
きっとあの子が
あなたとの出会いを
最高の運命だと -> gretest destiny/fate -> the best thing
感じていたからよBut it's really okaydon't you think there should be time for you to relax as well, Reimu?
でも
もう楽になっても良い頃合じゃないかしら -> This was really hard for me to translate... Someone might be able to come up with something more interpreative (preferably with a mention on opportunity/good time)
霊夢
Nevertheless,