What is this girl thinking?

While we were on the phone last night , she was over her moms friends house babysitting , and the womans oldest son came home and she started playing music with the volume high and talk’in flirtly with the the oldest son , then the oldest son got on the computer and she was like move let me sit down in a joking flirtly why . Then the son said’,”man you heavy “. Now I thought about it for a min and then realize she wa sitting on hes lap. So I say “if you get off that boy lap “.then she said she wasn’t she standing up. I was like dont lie 2 me . And she said iwas sitting on he Knee , but way you tripp’in Its not like I was sitting on he’s thing “, but I felt like she was advertising it. So we stayed on the phone argue’in And she told me if I would have said get off his lap and left it at that she would have actully listen to me , Because when I drag it out and stay mad at her all night . she just ignores me . But I feel like I should have never had to tell her not to sit on someone “Knee” in the first place . so what do you think she was thinking , And how should I go about handl’in this should I just let it go , try to understand her , or just let her do her , And I’ll just do me and we stay together?