"My mother can sing."
Translation:मेरी माँ गा सकती हैं।
Why is there a "hey" at the end here, but not with:
"She can not play."
Translation:वह खेल नहीं सकती।
In present tense sentences that contain 'नहीं', है ( है/हैं/हो/हूँ) is optional. I am not entirely sure why that is but I've heard that it is probably because नहीं was derived from some variation of ना+है so tacking on another है is redundant.