继承时如何重写派生类中的函数

我有两个类-母亲(基础)和女儿(派生)。我从母亲类继承了一个函数，并试图在女儿类中重写。它看起来像它覆盖，但我的困惑是，即使我不继承母亲类，函数仍然工作，所以我如何继承/重写它?我很困惑，好像我真的继承/重写任何东西。请注意在派生类中，我没有继承: public Mother谢谢你的帮助，一如既往!!

这是我的代码

Mother.hpp

#ifndef Mother_hpp
#define Mother_hpp
#include <iostream>
#include <string>

class Mother
{
public:
    Mother();
    void sayName();
    };

Mother.cpp

#include <iostream>
#include <string>
#include "Mother.hpp"
#include "Daughter.hpp"
using namespace std;
Mother::Mother(){}
void Mother::sayName(){
    cout<<"I am Sandy" <<endl;
}

Daughter.hpp

#ifndef Daughter_hpp
#define Daughter_hpp
#include <iostream>
#include "Mother.hpp"
class Daughter : public Mother
{
public:
    Daughter();
    void sayName();
};

Daughter.cpp

#include <iostream>
#include "Mother.hpp"
#include "Daughter.hpp"
using namespace std;
Daughter::Daughter() : Mother(){}
void Daughter::sayName(){
    cout << "my name is sarah" <<endl;
}

Main.cpp

#include <iostream>
#include "Mother.hpp"
#include "Daughter.hpp"
using namespace std;
int main(int argc, const char * argv[]) {
    Mother mom;
    mom.sayName();
    Daughter d;
    d.sayName();
    return 0;
}