There are a number of correct ways to say this. "Came" is correct. Or "I have come." Both are using the past tense because she has arrived at the house to see her son. So: She came to the house. Or she has come to the house. But you could use present tense too: "I am here to see my son." Or present partciple:"I am coming to see my son."　Ｓｈｅ　ｉｓ　ｓｔｉｌｌ　ｉｎ　ｔｈｅ　ｐｒｏｃｅｓｓ　ｏｆ　ｃｏｍｉｎｇ　ｔｏ　ｓｅｅ　ｈｅｒ　ｓｏｎ.