An internal examination is the gold standard for assessment and treatment of conditions related to the pelvic floor. Without feeling the muscles, your pelvic floor physiotherapist will be unable to identify if you have trigger points, or if you can contract your pelvic floor effectively.
That being said, there are generally many parts of the assessment and treatment that can take place without an internal exam. Some patients have been treated successfully without ever doing an exam.  Though the most benefit will be derived if your pelvic floor physiotherapist completes an internal exam, you will still benefit from pelvic floor physiotherapy if you are uncomfortable with or unable to have an internal exam.