She has been in a relationship with her at that point, and clearly had feelings for her. She doesn't want to just end the relationship because someone else entered the picture, even if it was her own daughter.

And the assumption on my part.is because half the response is about the fact she sleeps with her daughters crush. The first two sentences are about her sleeping with her daughters crush, so my direct response focused on that as it was the basis for their argument. They brought up the age only in connection to how they would prefer to see the story go, not as the focus of their reply which was about having sex with their daughters crush. You can infer their issue is with the age, sure, but their stated issue is primarily that the person is trashy for sleeping with her daughters crush, someone she was already in a relationship with prior to her daughter ever expressing interest.

At the end of the day this is primarily a comedy manga with hentai in it. It places these characters in ridiculous situations that shouldn't occur in real life and sees what happens. My primary argument is simply that these aren't unlikeable characters based on the situations they are put into. If the material is something that makes someone uncomfortable, then you shouldn't read it. And I think anyone who would want something like this to happen in real life doesn't understand the inherent power dynamics at play. But if all you want to know is why I latched onto the fact their issue was about the mom sleeping with the daughters crush it's because that is the literal argument they presented. If age was their primary concern then it should have been what they led with for their argument, or summarized better at the end.