
My Life with the Walter Boys Season 2, Episode 1 explained why Parker Walter is mad at Jackie Howard because of what she failed to do last season. As the only girl in the Walter household in the Netflix series, Parker is the family's princess, and she is protected by the Walter boys no matter what.
Parker (played by My Life with the Walter Boys cast member Alix West Lefler) thrived in the chaotic nature of living with her brothers, and she also adapted some of their interests, like football, leading to her tomboyish nature. However, Jackie's arrival at Silver Falls and in the Walter household changed everything for Parker, which led to initial tension between them because she is not used to having another girl in the house. Parker was skeptical about Jackie living with them because she thought of her as an outsider rather than family.
Parker feared that Jackie's presence would threaten her unique place in the male-heavy Walter household, so they barely interacted in the early episodes of Season 1. Despite that, it slowly changed during My Life with the Walter Boys' Thanksgiving episode, as evidenced by Parker accepting Jackie into the circle with small gestures, such as passing food and acknowledging her presence during dinner.

Parker and Jackie's sisterly bond truly manifested in My Life with the Walter Boys Season 1 finale during Will and Hayley's wedding. Parker was hesitant to wear a dress for the ceremony, confessing to Jackie that everyone would laugh at her because she would look stupid. This conversation is where Parker also admitted that the Walter boys "always make fun of [her] because [she's] a girl."
Jackie's honest advice to Parker about still looking great if she wears a dress hit different, and the pair's talk was the starting point for their true sisterhood. Unfortunately, it came to a full stop when Jackie chose to leave Silver Falls and return to New York in My Life with the Walter Boys Season 1's twist ending.
Jackie's abrupt departure from the Walter household without saying goodbye, particularly to Parker, fuels Parker's resentment toward her upon her return in My Life with the Walter Boys Season 2.
There is a reason why Jackie suddenly chose to leave. She kissed Cole during the night of Will and Hayley's wedding despite still being with Alex. Jackie left because she was confused and to prevent further chaos between the two Walter boys.
Did Parker & Jackie Resolve Their Issue in 'Walter Boys' Season 2?

Most of the Walter household is happy about Jackie's return to Silver Falls in My Life with the Walter Boys Season 2, except for Parker. She dismissed Jackie when she first met her back in the house, and the cold treatment continued mostly throughout Episode 1.
Jackie eventually apologized to Parker for leaving without saying goodbye and not staying in touch the whole summer. She also told Parker that she really missed her. Aside from apologizing, Jackie promised that she would try harder to be there for Parker as a true sister.
One way for Jackie to do it is to obtain her driver's license so that she can drive Parker around town and to her football practice, describing herself as Parker's "personal chauffeur." In a way, this could reduce Parker's reliance on her brothers and parents.
Parker was pleased with Jackie's promise, and she even admitted that she "kinda missed her too." Ultimately, they resolved their differences in the end and Parker accepted Jackie as her adoptive sister in Season 2.