Simplify the following text for a Grade 6 native English-speaking person.
Original: During the following night Grendel 's Mother arrived and Beowulf had an even harder fight against her , but he won .
Simplified: However , during the following night Grendel 's Mother arrived to avenge the death of Grendel and collect weregild . As Beowulf slept in a different building he could not stop her .