Brief Answer:
Allergic reaction

Detailed Answer:
Hi,

Thanks for your query.

I have seen the image you have attached here. The swelling in the lip your wife has is typically seen in allergic reaction. Such allergy can be due to food material or vegetable related allergens.

Zyrtec is the best remedy. The complete cure involves avoiding the allergen. Identifying the allergic is a difficult task. You may have to identify and avoid the allergen for few weeks or months for the reaction to occur never again.

Hope, I answered your query.

Wish you good health.

Regards,

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