If you don't like your maid and wish to terminate the contract, you can write this letter.
My current helper has a sister in the UK. Last April, she told me her sister would like her to visit UK for her holiday. Luckily, her sister in UK has a financial problem which cannot afford her visit. My helper cancelled her trip to UK. Later on, I was told by my helper's another sister that they were planning to send my helper to the UK for living. Because it is very hard to apply visa in Phillipine.
So if you write a letter for your helper, you are prepared to face a lot of problems. There is no way that you would know the true reason why she needs the letter.