Depends what she's said and what the company'svpolicy says. If she's been publicly critical of the company, or defamed another member of staff, then this could be gross misconduct and you don't need any warnings to be dismissed for gross misconduct
So she's been wasting time at work and has now bad-mouthed her boss on FB? Is this your daughter's first job? Yes, I think she could very well lose her job as a result of this, particularly if she works in a role which can easily be refilled.