I can't make out which is her principal residence on the website. It sounds like Windsor Castle is mainly a weekend retreat.
Buckingham Palace
Buckingham Palace has served as the official London residence of the UK’s sovereigns since 1837 and today is the administrative headquarters of the Monarch.
Windsor Castle
A Royal home and fortress for over 900 years, Windsor Castle, the largest occupied castle in the world, remains a working palace today. The Queen uses the Castle both as a private home, where she usually spends the weekend, and as an official Royal residence at which she undertakes certain formal duties.
www.royal.uk