Could anyone help me to check if it is correct?

I need to write a letter to confirm one's English ability. But I don't know if my writting is right? Could anyone who is good at English to help me to check and modify it below??? Many thanks!!!

(This letter serves to confirm that XXX has excellent written and verbal communication skills in English.

Due to XXX working environment, XXX is required to use English as her basic language at all the time. School staff and students are all English speakers. School papers, reports and newsletters are also written in English. XXX listens, motivates and advises her students very well, and also passes her knowledge to the others clearly and correctly. Her English proves that she is an excellent English speaker.)