I am Athy's older sister??? Oh well

the cover does not belong to me
What if Anathasia had an older sister?
What if Claude got Diana pregnant in a one night stand and she gave birth but was informed that the child died.
What if Claude neglected the kid and gave her a palace in a forest far away from him and diana.
What if Diana saw her first child while she was strolling in the garden after she had an argument with calude about the child she was carrying.
What if the older sister was sent to war by Claude (who thought she was a boy).
What if the lone girl met the new people, people who cared and loved her.
What would happen when Claude calls her back when she turns 14. Would she resent him for abandoning her or accept him or would she just give her life away for the sake and happiness of her younger sister.
Is a crossover of:
WMMAP x I became the wife of the male lead (fiona is not transmigtted) x TCF
P.s. This is the Athy from Wmmap and Diana will die after giving birth to Athy.