Thanks for asking the query,
Difficulty in opening and closing of the mouth can be due to muscle spasms.
I would suggest you to give her muscle relaxants.
Take a towel dipped in warm water and apply on her TMJ
on both the sides for 3-4 times a day.
Do warm saline gargles 3-4 times a day to give a soothing effect.
Take a soft diet
Maintain a good oral hygiene
If the symptoms persists or even worsen visit to the concerned Dentist
and get the checkup done.
Hope this helps out.