And, most importantly, whose side are you on?
The answer is hidden in the comics: not so much in Titania's origin story but rather in her journey to superpowers. In the Marvel Universe, she started off as Mary MacPherran – a girl from Denver, Colorado, who was bullied in school by popular "mean girls" and only had one friend, Marsha Rosenberg.
This friend, however, shared Mary's obsession with superheroes. The two were fantasizing about getting superpowers one day; once, Mary even started to claim that she was a Spider-Woman (mimicking the actual Spider-Woman who showed up in town). She told Marsha about it, only for the latter to spread the word – and suddenly all the mean girls wanted Mary in their inner circle. With her "superpowers", she was a welcome guest in places where she had faced nothing but bullying before.
However, Mary was in fact just a step away from obtaining actual superpowers – with the help of Doctor Doom, who, according to the comics, chose Mary and Marsha as his soldiers for the Battleword (a dimension created by the Beyonder for 'Secret Wars'). Her friend got lava superpowers and became Volcana, while Mary was upgraded by Doom to become Titania – an extraordinarily strong and muscular superhuman.
Alright, you might say. What does it all have to do with Jennifer Walters, a not-so-regular and occasionally green attorney?
It's amazingly simple. Titania just hates the fact that She-Hulk is the only person who can compete with her when it comes to strength.
Yep, that's it. The rivalry between the two is motivated by no such things as revenge or higher purpose. It's not even the notorious "I blame Tony Stark for this" reason.
However, one has to keep in mind that 'She-Hulk: Attorney at Law' might alter Titania's story for the sake of the MCU lore. After all, 'Secret Wars' as a premise of Titania receiving her powers, has simply not happened in the cinematic universe yet.
This is why Jameela Jamil's supervillain might have a deeper and more meaningful reasoning for her bad blood with Jennifer Walters. Or, on the opposite, even less of a reason to actually go against She-Hulk, at least according to some of the Reddit fans:
"Titania is clearly not the main villain of She-Hulk. Her whole motivation is just to sue Jen for vain, superficial reasons. She may briefly side with a more bad bad-guy, but by the end of the show she’ll probably be portrayed as a comedic antihero like Swordsman and Razor Fist. Hell, I think she has a good shot at joining the Thunderbolts if audiences respond well to her." - /metal_signal17
We'll get to know more when 'She-Hulk' premieres on Disney Plus on August 17.