I am sorry to hear about your daughter's anxiety.
You could suggest Passiflora Complex as this is traditionally used for stress and anxiety and where there may be digestive stress and palpitations.
It is fine for teenagers and can be taken for as long as needed.
Flower Essences can often be helpful where emotional distress is present and this can be taken with the Passiflora whenever she needs something 'on the spot'.
I would suggest either Relaxation Essence or Emergency Essence.
Do you have questions? Please feel free to ask.
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