First of all: Thank you for your work and although there's some small stuff, it is absolutely readable. Please don't feel discouraged by me going though the story with a fine-toothed comb.
Second: I'm not a native speaker as well but I'll try to catch as many errors as I can. There's a lot of small, mostly grammar stuff.
Page 1, first panel: "Heroine", as mentioned already
Page 1, second panel: "when even an [Attendant] seemed unreachable" (P.s. I'm not really happy with this as well, it still sounds wrong somehow)
Page 1, third panel: "Though Otou-sama didn't say it clearly", "Whenever my bride lessons came to a break, I ended up going to the back yard to train"
Page 2, second panel: "Just a bit until your Highness, the Demon Lord-sama, gets/is reborn."
Page 3, second panel: "I need to reach the other side of the wood!"
Page 4, fourth panel: "Ugh, it's hurting/it hurts (sounds a bit more natural imo) so much..."
Page 4, seventh panel: "What is the reason for you to seek power?"