character letter of support toImigration director for my sister

Hi,
I need help with writing a letter to the immigration director in suppor of my sister so she can stay in the country.The letter is due this week so please please help me

She's been here for almost 19 years. She is the smartest of all, very good charachter.
She is a very good sister and eventhough she is 4 yrs younger than me she is wiser and a person I go to for any question.
While in US she finished college and is in process of getting her Mastesr degree in engineering. Has a very good job and is doing great in that aspect
We live in different states but I go visit her with my 4 kids at least twice a year, or whenever my kids have a longer than a week off school. She also helps with tickets when we fly.
While visiting her we stay at her house she takes care of all expenses for my family. On top of that she supports and takes care of my mother who is 73 yrs old. My mom doesn't work, doesn't have any income, does not drive, doesn'rt speak any english and can't do anything on her own. My husband is the only one working since I have four kids, ages 13-15. So thinking about taking my mother under our roof is really not a joice or solution. This is another reason I have to keep my sister in the country.
I could really go on and on to prove her good character and to prove that she needs to stay here if for nothinbg else for the burden that would fall on me if she was to leave (get deported)

Thank you. Lisa