There's a great deal of misinformation about Maria Gaetana Agnesi online. One of the reasons I created this site was to point out some of those errors. Today, though, I'd like to share a website that sticks to the facts: the MacTutor History of Mathematics Archive. The site is hosted by the School of Mathematics and Statistics at the University of St Andrews, Scotland. I was pleased to discover that the MacTutor biography of Maria Gaetana Agnesi is based on information from reputable sources, and it includes a list of those sources.
Here's the portrait of Maria included in the MacTutor bio (which is in the public domain):
I commend Edmund Robertson and John O'Connor, the creators of MacTutor, for a job well done!