I let her cry however she keeps on making herself vomit through crying so hard
This is probably a lot of the cause of the current problem. Then when leaving her to scream didn't work, you bought her into your room. So now she knows if she screams for long enough you will bring her into your room.
Leaving her to scream isn't the answer for a 2.5 year old toddler. But there's been an element of trust destroyed since uou did leave her to scream enough for her to be sick. So it's going to take gentle patience and time to move on from this.
Firstly that means not leaving her alone to scream. She can (and probably will) scream in frustration. But she needs to know that you care, haven't just abandoned her and left her alone and most importantly that your boundaries are immovable
So tomorrow explain that she will be sleeping in her room tonight. All night and that you will stay with her until she is asleep.
So some playing in her room today. Play together on her bed. Maybe have a picnic together on there.
Then at bedtime, do your normal bedtime routine and you lie down on her bed or next to it with her. Have a mantra and done deviate from it:
^"Sleep time now, we lie down quietly on our bed at sleep time. Nan night"
That need be the only thing you say, over and over again. Keep returning her to bed, keep lying with her, keep cuddling. M9st importantly, keep your boundaries clear and don't give up. Keep going relentlessly until she is lying down in bed asleep
Yes, it may mean you get very little sleep yourself. Just try to find ways to catch up on sleep the next day.