Dear Ms Ma,
敬爱的马老师：
I apologize that I cannot go to school today.
很抱歉我今天不能去上学了。
Last night my mother had a high fever and coughed badly. I think that she has got flu.
昨天夜里我妈妈发高烧，咳嗽得厉害，我想她可能是得了流感。
She didn't have a good sleep and is very weak today, so I will go to Tiantan Hospital with my mother, and then stay at home to attend her.
昨天晚上她休息得不好，而且今天很虚弱，所以我陪妈妈去天坛医院，然后在家照顾她。
Because of this I have to ask for leave.
因此我不得不请假。
I will appreciate you very much if you can allow my leave.
如果您能准假我会非常感激。
Yours, Li Li
您的学生 李丽