Because Slutbag Linda is a drug-dealing, sex trafficking, prostitute. Plus she had Jeffery Epstein murdered in his cell on Rikers Island. You know nothing about the "real" Slutbag Linda apparently.
You fill in the blanks how you choose to and I will fill in the blanks how I choose to.
But as far as the actual text goes. Slutbag Linda is the only fucking a different dude in the bed she shares with her husband. At the same time, as her husband is actually sleeping in the bed at the time. Slutbag Linda is the only one showing off her daughter's ass to the pervert MC as well. In my book that makes Slutbag Linda a slutbag and Celia as just a frustrated freaky housewife. BTW, Celia was an unwilling sexual partner of the twerpy MC. Whereas Slutbag Linda pursued the MC of her own free will. Gleefully cucking her husband, good guy Bob to boot. Lastly, if you play with incest. Slubag Linda is fucking her own son, Celia has no blood relations to the MC. What a Slutbag, Slutbag Linda is.