Translation:She writes with her left hand.
from wikipedia :
Specifying Chinglish to mean "Chinese words literally translated into English", an experiment in linguistic clarity found that mathematical terms are more readily understandable in Chinglish than English. English words for mathematics typically have Greek and Latin roots, while corresponding Chinese words are usually translations of neologisms from Western languages; thus quadrilateral (from Latin quadri- "four" and latus "sided") is generally less informative than Chinese sibianxing 四边形 (literally, "four-side-shape"). For example, compare the semantic clarity of English axiom, Chinese gongli 公理, and Chinglish (literal translation) "universal-principle"; median, zhongshu 中数, and "centre-number"; or trapezoid, tixing 梯形, and "ladder-figure"
Or to further this, it would be used if "the hand" was something more significant. Everyone has a hand, it's not special. You have to specify what hand... that hand, this hand, her hand. The only time you wouldn't need to specify would be if it was something significant.. like THE HAND OF GOD, or something like that.
Probably a more "normal" usage to demonstrate this: she uses HER computer. She uses THE internet.
As you eluded to, the only way around this is to have sufficient context that adds significance to the particular object you're describing. Only then would you say she uses THE computer.
There is nothing "wrong" about your sentence. It simply is not as strong as it could be.
even if you consider this a "Wright answer" this English ie Wrong: she uses left hand to write" is wrong! You guys really have to review your English if you want your Chinese course to be credible! We already know that you don't care about our comments but you really have to do something about this! There are plenty of similar issues throughout this course that to this day are not dealt with... Takes months to solve, as it seems....