Depending on how you play the Madam will always urge her to give up adventuring, risking her life or body and just work at the brothel full time for extra money. If you fail loads of quests she gets frustrated because she doesnt want Serena to destroy herself. Eventually she ceases her priority at the guild so you get less money and have to work at the brothel. If you start working full time she reacts positively to you for obvious reasons.
But when she got killed I reckon it was Ganelon and his cronies that climbed up the building via ladder and slaughtered her because Ganelon had his own brothel and didnt want competition.He probably heard Serena also worked there and wanted her body. Serena also showed sorrow for her death
I like how their interaction shows that Madam is actually good at managing people. If you kept failing she will still call Serena, but eventually stop nagging at her and just ask her to go, just to show others that 'she scolds people who keep disobeying her', yet know that serena is stubborn, and just hoping that she'd stop doing useless things(like adventuring and failing).'
And if Serena did not fail any adventuring job, Madam does not reprimand her.
And know that madam actually treats it as 'giving' serena 5000s, because when Serena actually pays her back, she said she did not expect anybody to return her owed money and was surprised. And after Serena paid her back, she still let Serena sleep at her place, for free.
I see Madam as a soft-hearted person, yes she gets girls to work as a prostitute, but even a prostitute can make money at the end of the day, and it's a relatively safe job, and be self-sufficient. And working as a prostitute under her is better than being treated as a cumdumpster for Ganelon. In a way she is protecting the girls under her, Serena included.
Probably it is as you said, Ganelon is the one who killed Madam, since the scene ended(?) with Cecila and Serena both pregnant and serving Ganelon, making Cecila unable to investigate any further.
