Philamena Dinallo, who lives at Clara Court Residential Home, in Courthouse Road, Maidenhead, was born in Bagshot, Surrey, in 1911.
She left home at 13 to live with a family between 1924 and 1966, looking after their children and working in a bakery. When the family moved to Westcott, Bucks, to run a pub she moved with them to work behind the bar, before living with her sister.
Andrew Glass, 88, who was looked after by Philamena when he was three, helped celebrate her birthday. The horse racing fanatic marked her centenary at the home she moved to five years ago.
Niece Loretta Apperley, of Surrey, said: "What she didn't know about horse racing wasn't worth knowing."
Philamena celebrated receiving her telegram from the Queen with her niece, three nephews and a 90-year-old cousin.
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The Met Office has issued a yellow alert for Windsor and Maidenhead, Slough and Wokingham, warning that rain moving eastwards across the south of the country may turn to snow in some places.