alumna
A woman who has graduated from a particular school or college.
An alumna is a woman or girl who graduated from a particular school, college, or university. If your older sister graduated from Lincoln Elementary School, she's an alumna of that school. When a famous writer visits a college to give a talk and mentions she studied there twenty years ago, the college might introduce her as “a distinguished alumna.”
Today it simply means a female graduate. The male version is alumnus, and when talking about a mixed group of graduates or multiple female graduates, people often use alumni (which technically refers to men or mixed groups) or alumnae (for multiple women only).
Many schools stay connected to their alumni through newsletters, reunions, and fundraising. When someone donates money to their old school or helps current students find jobs, they're acting as an engaged alumna. Schools take pride in successful alumni because these graduates represent what students from that school can achieve.