First we have to understand the reason for the swelling.Common reasons are infection
due to depositions of food , trauma to the tooth or broken tooth.
(trauma is a accidental damage to tooth internally while eating or if some one fell down etc )
Remedies : She has to go for Antibiotics and this will be given based on her age and health conditions .For temporary relief she can use Ketarol DT (Tablet).
Put in tablet in a glass of water and once it get dissolved she has to drink.
The first important thing is she has to consult a dentist
immediately and get some antibiotics and doctor will prescribe this post evaluation.