I think the last sentence of the summary is a bit too long it contains three commas so the sentence reads a little bit difficult for me. I also think the summary could have a bit more pazzaz to match the story.
I'd write it like this:
Amèlia dies and gets sent to Hell, where she has to work under the first and famous Prince of Hell, Lucifer, to pay for her sin of pride.
The glamorous prince plans to make a grand return and conquer Heaven for all of demonkind. But how will he pull off such a large-scale conquest?
This is just an example I wrote but I tried changing it up a little and add a little more spice to it. You could also add how Amèlia aids Lucifer in this or what role she plays in it.