what if tho...

yeahh that could be possible but she absolutely has like no backstory or important details abt her,, but i can definitely see her being connected with rciel 。(*´꒳`*)

I agree with you, Jane definitely gives off a meanie vibe ! But a meanie that might turn into an ally, am I the only one feeling this ? Maybe I am optimistic x)
I also have been thinking she might be a boy actually, may be I'm going too far haha...But the way she's drawn, her traits and expressions, I feel something slightly masculine... But maybe that's just her charachter and I'm only fantasying on gender-bend x)

Eh, probably not.
One thing the twins have in common is that their servants have undying loyalty to them for some reason or another. OCiel gave his servants new purpose and new lives, so that's obvious, and RCiel's star servants/Undertaker are also shown to be extremely loyal for reasons not yet revealed.
Jane works solely for the money and dips when she's outmatched. Dealing with Mey-Rin and Ran Mao wasn't worth losing her life, nor was it worth the paycheck; that's why she left. She'd have to continue dealing with them if she was on RCiel's side, combined with Finny, Snake, Bard, Sebastian, etc. Not worth her time or her life, even if she was paid well. She's an interesting character, and I'd like to see her again, sure, but she's probably not on either twin's side.

ok i see you pointヾ(❀╹◡╹)ﾉ~

I read a really interesting theory about how Jane could be actually John Brown who is actually a demon as well and is currently investigating the blood collecting cases too hence why Jane was quick to quit her job lol

i once thought about john being a demon too! but my theory had too many holes so i gave up ╮(￣▽￣)╭