Sword!
Beowulf followed Grendel's mother's tracks to her underwater lair after she attacked Heorot. He dove into the lake and ultimately battled and killed her with the help of a magical sword he found in her lair.
he dies later on
Under water, where Grendel's mother lived.
While fighting Grendel's mother Beowulf finds his sword does not work against the monster. He discards it and takes Grendel's mother's weapon. Most men would not be able to lift it. He then beheads the monster.
Beowulf kills Grendel's mother by using her own weapon, a giant's sword, against her. This is ironic because he defeats her with the very weapon she was planning to use against him. Additionally, he avenges Grendel's death by killing his mother in the same manner that Grendel killed Hrothgar's men.
The dragon is beowulfs song which most people don't' know cause it doesn't really tell you... and the golden horn Beowulf got from the king is a symbol. If Grendels mother has it he shall not attach but it soon comes back to it's owner and it comes back to Beowulf when he becomes king. So Beowulf and Grendels mother got to gather and he gave her another son, he just couldn't help it. so Beowulf really doesn't kill Grendels mother he just says he does.....
While Grendel's mother is hard for Beowulf to defeat, he IS able to use a sword, where as he has to battle Grendel bare handed.
No, Beowulf's mother does not kill Unferth in the epic poem Beowulf. Beowulf defeats Grendel's mother in battle, but Unferth is a Danish warrior who is not directly involved in that fight.
After Beowulf harms Grendel, the mother breaks into the hall to take his arm home. Beowulf is told by the king that htere are actually two monsters. Beowulf leaves at once to go underwater to kill Grendel's mother.
Beowulf discovers that his sword is ineffective against Grendel's mother's tough skin. He discards the sword and instead uses a magical weapon found in her lair to defeat her.
Beowulf dives into the lake where Grendel's mother lives and swims down to her lair. There, he engages her in a fierce battle using a magical sword that he finds in the lair. Beowulf eventually defeats Grendel's mother by decapitating her with the sword.
Fighting Grendel, Grendels mother and the dragon once he returns home to Geatland and is crowned king.