To determine the most probable poison consumed by the 14-year-old girl based on her symptoms, let's analyze the details provided:

• Bradycardia: The pulse rate is 52/min, which is slower than the normal range for her age.
• Hypotension: Blood pressure is 100/70 mmHg, which is relatively low.
• Respiratory Depression: Respiratory rate is 8/min with shallow breathing.
• Cold, Clammy Skin and excessive salivation: These are symptoms of increased parasympathetic activity.
• Crepitations on auscultation: This occurs often with increased secretions in the lungs.
• Flaccid paralysis and fasciculations: These are signs of neuromuscular transmission issues.

These symptoms align well with poisoning due to Organophosphorus compounds, which are known to inhibit acetylcholinesterase. This results in an accumulation of acetylcholine, causing symptoms such as:

• Increased parasympathetic activity: bradycardia, hypotension, excessive salivation, wheezing/crackles due to bronchorrhea.
• Neuromuscular effects: fasciculations, paralysis, and respiratory depression.

The other options do not match the symptomatology:

• Barbiturates: Typically cause CNS depression, decreased respiratory rate, and hypotension but not the widespread parasympathetic symptoms seen here.
• Copper sulphate: Causes gastrointestinal irritation, hemolysis, and renal toxicity but lacks the neurological and parasympathetic signs.
• Opioids: Cause CNS depression and miosis but do not cause parasympathetic overactivity or fasciculations.

Therefore, the clinical presentation is most consistent with Organophosphorus poisoning.