I get the strong impression Big D was absolutely livid with her results and that’s why she’s so obsessed with them. Her whole life seems to be oriented around the contradicting goals of impressing him while also trying to prove a point by “taking her own path”.
Maybe Mama E was displeased too, maybe she was supportive who knows - Jack doesn’t seem to have anywhere near the desperation to be approved of/prove wrong/get attention from her as she does her father.
I think her family were livid for her for a number of reasons: the GCSEs, the young single pregnancy, the (likely) behaving very badly at the fire service making her a pariah.
This is all fairly standard parent stuff imho. I only have sons but tbh if I had a daughter who got pregnant at a young age before she was qualified, or financially independent, with no career plans and no relationship, I'd be livid too. Not because I'd think she was a harlot who shoulda kept her legs shut but because I'd be frantic with worry about how she'd support herself, how she'd fulfil herself educationally and in her career, and whether it was the right set-up for an innocent child to flourish. My lividity would be the result of love, in other words.
Likewise if I got one of my kids a coveted well paying job at my firm and they (as I suspect Jack did) fucked it off by having a bad attitude, poor time keeping, and then flounced, I'd be utterly mortified, and yes, again, livid. Not because I'm siding with der ebil firemenz against the bird who wanted to wear traaaaazers, but because it reflects badly on my career prospects and thus my ability to support my family including my ungrateful daughter. Again, my anger would be born out of love not spite.
Jack doesn't understand this and despite having a kid herself, doesn't seem to comprehend the sacrifices that parents routinely make for their children (which I've always found odd in itself). Hence the entire rest of her life has been an extended teen rebellion of "Mum! Dad! Look at meeeeeeee! Look how counterculture and edgy and rejecting of her values I aaammmmm!!!" even tho deep down she's cut from exactly the same cloth of net curtain twitching narrow minded middle class suburbia.