A Picky Plant
Bellie is both snobbish and blunt, unafraid of being direct and giving people her opinion of them. She comes from a life of living with the "haves", and doesn't think all to highly of the "have nots", which often has her feeling that a lot of people are beneath her and not worth acknowledging. She is also superficial, in that she measures people with arbitrary factors such as how much money they make, how much power they can command or even where they were born. She disregards Nidorina alone for being born into a flyover state full of sodbusters and manure shovelers like Montana, instead of the vastly superior coastal state and entertainment leader of the world, California. There's plenty of other reasons why she doesn't like Nidorina, as well, and the two of them do not get along at all. Bellie also does not play nice with Bulba, as she gets in the way of Bellie's off and on interest in Bellsprout.
As a fighter, she has excellent skill, and is stronger than Bellsprout. This is mostly due in part to the militant training regimen that Son of Nightmare puts all his Pokemon through, while Bellsprout has to self train by and large. She also has the strength of a Victreebel now condensed back into the form of a Bellsprout. Shortly after Bellie and Bellsprout broke up, Bellie trained with Son of Nightmare fast to evolve all the way through to a Victreebel with the help of a Leaf Stone. Upon reuniting with Bellsprout again, everyone was too uncomfortable with her then new form to be around her, and Death Reaper JOE reversed her form back to a Bellsprout while still retaining the statistical benefits.
She respects Son of Nightmare because he is already powerful on his own (and Bellie respects power), but also because he is very competent and knows how to make those under him more powerful themselves. There was no way for Bellie to pass up an opportunity have more power for herself, as she could use that power to gain more influence for herself, as well as for her own protection. A thirst for power aside, Bellie is very girlie-girl otherwise and likes to partake in the usual stereotypes such as shopping and watching reality drama on TV. She is also a socialite and likes to attend parties and mixers where she can.