में उससे पत्र लिखवा रही हु । vartani(spelling) correction मैं उससे पत्र लिखवा रही हूँ | a female is saying that "i am making him/her write a letter" मैं - I उस से - from him(her) /by him(her) उस can be used to denote both male and female पत्र -letter लिखना - to write लिखवाना - to make someone write. (someone writes because the other asks/force/make him/her to write). रहा रहे रही in this type of usage denotes continuous tense if hai (or hoon or ho) (hain after rahe) comes after these (i.e. रहा रहे रही), sentence is present continuous, if tha/the/thi comes in the end means sentence is past continuous.

it simply means"i am making him/her write a letter"