Will it affect the health of the baby?

Hello everyone,
My sister is 4 months carrying and is suffering from severe back pain. Due to the back pain, she resigned from her job and is now at home. As per the opinion of the doctor, she started performing prenatal yoga as it is one of the best ways to lessen back pain.
One of my friends told me about physiotherapy is a very good solution for back pain. I found this clinic offering physiotherapy treatment. But can it be tried during the pregnancy period? Will it affect the health of the baby?
Please do chime in your suggestions.