Seriously, these are very end, all memories gotten spoilers.
I just started a second play through and got to Kakariko (after learning that you can't activate Robbie's furnace without talking to Impa and Purah, in case anyone was wondering lol) and was directed to the first memory. Clearly you could go to any memory, but they direct you to the one outside of Lanayru Road East Gate first.
So the memory there is one where Zelda returns from the Spring of Wisdom and has no luck and, immediately following, the moment Calamity Ganon returns. What I thought was interesting was that Mipha starts to say something like, "This might be dumb and not help you unlock your sealing power, but the thing I think about when I'm healing is – " and Ganon returns and cuts her off.
If you've seen the final memory where Zelda unlocks her powers, you see that her care for Link is what unlocked her sealing power (her love for Link really – her attitude towards him certainly seems like she could love him, her diary shows her opening up to him, and Kass' final song mentions how she was in love with Link and how her love for him unlocked her power).
SO I'm assuming Mipha was going to say something like "thinking of the person I love" (who was also Link of course), which wound up being the solution. In fact, Mipha probably thought specifically about SAVING Link, which is what Zelda does to finally unlock her powers.
I just thought it was a cute touch that Mipha is about to tell you in the first memory how Zelda will unlock her powers in the final memory.
(Another note about Zelda's memory – I wonder if she sealed the part of Ganon in most of the guardians in that graveyard (and maybe somehow managed to do that for a number of other guardians throughout the world) since they remain dead and never return with the blood moon. In the memory, there are guardians that are already dead and I wonder if those are the ones that actually come back to life after the blood moon)
(Man I just really love that last memory, I've watched it so many times. It's just so cool.)
tl;dr – Mipha knew the secret to unlocking the sealing power in the first memory you get, but doesn't get to say it. Also, did Zelda kill-kill a bunch of guardians?
tl;dr of tl;dr – this game is just so great