My sister will probably have finished her homework by the time she goes to Hokkaido.
Literal
Younger-sister [topic-は] Hokkaido [to-へ] go [by-までに] homework [object-を] finish-doing will-probably.
~までに ('by the time') marks a deadline. やり終える ('finish doing') is a compound verb — やる ('do') + 終える ('finish'). ~ているだろう projects a completed-state into the future: 'will be in the state of having finished.'