I agree wholeheatedly with AF's response, expecially "She's out buying presents"

. In addition, with regards to c), if I am upset, I might use, "I will leave this room". 'will' expresses a strong intent. Otherwise, I'd use, "I'm going out (now)" or "I'm leaving now." If I'm not at home, I wouldn't use the former, "I'm going out (now)." I'd use, "I'm going/leaving (now)."