Thanks for posting your query,
This may be due to yogurt allergy
only or allergy to certain milk which yogurt is made of( if she is allergic of cheese and other milk products as well)
the severity depends on presence of one or more of these allergic symptoms:
One suffers from hives.
Skin becomes red.
Difficulty in breathing.
Symptomatic of anaphylaxis
, which is a life-threatening condition
you should do the following to avoid this allergy:
avoid milk and milk products.
be careful while taking food outside.ensure that the food items do not contain any yogurt.
Read the label to ensure there is no yogurt in the product.
give her soy milk or soy milk products
and it would be better to council an allergist if the case is not improved
wish you good health