Sorry if the game did not communicate this properly, but if the Lamia is casting the seduce spell, then Amelia is seduced and cannot escape. When you 'Refuse' the spell about 3 times, the seduce will end and this event will change into a stomach squish event instead.
So it's impossible for you to escape because Amelia is seduced. Get Amelia's stats in the correct range and only select Refuse. Also read the tip page for Lamia in: Help > Predator Tips - Spoilers. I try to explain the 'puzzle' involved with each predator there, if any. If the tip page does not explain it well enough, I can consider changing the wording a bit.