Thanks for the answer Star!
I actually thought about restarting on Normal because Hard was giving me so much grief. However, I realized that part of it was me being unhappy with MU's strong stat, so instead I restarted on Hard Classic again but this time making the strong stat magic, since I was leaning that way with her anyway. Now she's a beast and one of my highest level characters. I mean, a strong magic user with above-average defense? Yes please!
On chap 5 now, but thinking about doing Florina's DLC fight next for the EXP. After looking at the official character list and this thread, I'm rethinking some of my pairings. The Miriel/Vaike pairing seems cute, but I'm kinda thinking about what Lucca said and leaning towards the Vaike/Lissa pairing. I was thinking Miriel/Kellam might be interesting to see, or maybe Miriel/Lon'qu.