L.L.
well for 2.5 years she's been sleeping in your bed, so of course she's going to have a hard time transitioning. You can't bring her to bed with you anymore- you have to stick with a routine. Kids thrive on routine which is why she's not sleeping well for you now, you keep bringing her back to bed with you.
Come up with a plan and stick to it. I would just keep going in to comfort her when she wakes up, but that's it.
She will eventually sleep thru the night if she knows she doesn't get to go into your bed.
Good luck,
Lynsey