@Sasha L. Sallie - Respectfully disagree. Your situations are not similar, unless OP is leaving out information. She states she hasn't worked in 4 years and is collecting food benefits. She has no income, therefore she has no benefits from not being claimed as a dependent. She would not get a tax refund if she filed on her own.
The ONLY situation this would have been beneficial is the stimulus checks, of which NO ONE knew was going to happen. At this point, even if they haven't filed their taxes, their info wouldn't get processed before the next check is issued, so she still wouldn't get a check because they will end up using last year's information.
Plus, if she hasn't worked and her parents are supporting her, they are entitled to the benefits they get from claiming her.