Well, even if she can't swallow the tablets or they come up, there are buccal tablets that dissolve on the gum line next to the cheek or sublinguals that dissolve under the tongue that can help with nausea and vomitting. Kids can take tablets though.
Encourage her to go to speak with her GP with support of your parents. Most people don't like seeing their doctors, but life isn't always about doing what you like, particularly when health is involved.