I'm sorry your little girl isn't feeling well
Unfortunately, I doubt this as simple as getting a seed stuck--this sounds like vomiting, which can be very serious. It could be anything from an upset stomach (Has she had any new foods lately?) to an illness or infection.
At the moment, it's important you separate her from the other budgies since she's still looking sick and keep her warm. You can wrap a hot water bottle in a towel and place it at the bottom of her cage in case she needs it.
Also, it's important to keep her fed and hydrated--since she may not feel like eating or drinking, to pique her appetite, soak some millet in electrolyte solution like sugar-free Pedialyte or some homemade electrolyte solution and see if she'll eat that. You can also give it to her in place of water.
Here's a recipe if you need one:
Meanwhile, you should monitor her very closely, and if she doesn't perk up within the hour, you should really take her into an avian vet for proper diagnosis and treatment for the best chance of recovery.
I hope Chippy feels better soon! Please keep us posted