EXACTLY.

EXACTLY.

it isn't just that "Vi thought Jinx left her in that cell", it's more than that

in a really short time, Vi thought she had both Jinx and Vander back, briefly hoped she might get Caitlyn back, then lost Vander again, nearly died, and woke up to the news that after all that progress things were back at the start 6 months prior, that she was going to have to get between Caitlyn and her sister again and possibly lose both again

she didn't get down to Jinx's cell with a rational plan and a clear head - she was desperately clinging to the last hope she had to make things right (in her head, right meaning = having both Jinx and Caitlyn in her life)

yes, she thought Caitlyn would be angry at her, but she also hoped that if Jinx redeemed herself in the eyes of Piltover, she might redeem herself in Cait's eyes too somewhere down the line

was it a good, rational plan? nope. but at that point Vi was one Warwick away from having a complete mental breakdown herself and she was running out of time (the war with Noxus being on their doorstep and all)

and then, not only did Jinx reject that plan, she punched her and locked her in that cell, separating them again. It doesn't matter what words Jinx used in that moment, doesn't matter what she said - Vi could hear her words, see her attitude, but she wasn't in the headspace necessary to listen. She was too caught up in her own grief and despair to pay attention!

she had been clinging to one last hope and she lost it - thought she had lost everyone, for good this time, and that it was her fault. she was basically back in prison (literally thanks to Jinx, but this was also pulling her back to how she felt after her initial separation with Powder in S1)

really, it's no wonder she had such a strong reaction to Caitlyn afterwards