Two cans of a "normal" energy drink is less dangerous than a cup of brewed coffee of 350 ml (12oz) - in terms of caffeine.
According to Medscape
Caffeine has differing CNS, cardiovascular, and metabolic effects based on the quantity ingested. Average doses of caffeine (85-250 mg, the equivalent of 1-3 cups of coffee) may result in feelings of alertness, decreased fatigue, and eased flow of thought. High doses (250-500 mg) can result in restlessness, nervousness, insomnia, and tremors. In high doses, caffeine can cause a hyperadrenergic syndrome resulting in seizures and cardiovascular instability.
According to Wikipedia referencing Factors Affecting Caffeine Toxicity
The LD50 of caffeine in humans is dependent on individual sensitivity, but is estimated to be about 150 to 200 milligrams per kilogram of body mass or roughly 80 to 100 cups of coffee for an average adult
According to The BBC
Use this guide for the amounts of caffeine in products:
- One mug of instant coffee: 100mg
- One mug of filter coffee: 140mg
- One mug of tea: 75mg
- One can of cola: 40mg
- One can of energy drink: 80mg
- One 50g bar of plain (dark) chocolate: around 50mg
- One 50g bar of milk chocolate: around 25mg
If the above is correct, two cans of energy drink is a lot less than a lethal dose.
Given an average body weight of 80 Kg, the LD50 is 12000 to 16000 mg which is 150 to 200 cans of the above Energy drink.
A girl aged 14 might weigh only 50 Kg, a thin girl maybe only 40 Kg. Therefore LD50 = only 6000 to 8000 mg which is 25 to 33 cans of an unusually strong 240mg/can drink. So 2 cans is a lot but not a lethal dose for most thin 14 year-old girls.
Obviously some people are more sensitive than others and will have complicating factors such as high blood pressure or other existing medical conditions.