Here's a good bit of trivia: She played Laverne in 6 different TV series - The character first appeared of course in Happy Days, got spun off to Laverne & Shirley (Shirley having the double Happy Days connection of her character being introduced there, and Cindy Williams having also appeared with Ron Howard in American Graffiti), she also appeared in the pilot for fellow Happy Days spin-off Mork & Mindy, she appeared in one episode of a short-lived sitcom called Blansky's Beauties, and then was also in (with Penny Marshall's voice work) two Saturday morning cartoons based on Laverne & Shirley and Mork & Mindy. Penny Marshall also had a recurring character in The Odd Couple, so she was a very familiar face to people who watched TV in the 70s or those of us who watched syndicated TV in the first half of the 80s.
Her only directorial effort I've seen was Big, but she also directed Jumpin' Jack Flash, A League of Their Own, Awakenings, and The Preacher's Wife, which were varying levels of success. Her other films seem to have bombed at the box office. Riding in Cars With Boys was her last feature film (with Drew Barrymore and Steve Zahn), and her last directorial effort has yet to be released, a documentary/bio-pic on Dennis Rodman.
One more interesting tidbit: her brother Garry gave her her first shot at acting, putting her in How Sweet It Is! with Debbie Reynolds and James Garner. She also appeared in a commercial for a dandruff shampoo with Farrah Fawcett...you can guess how she was cast there, since Fawcett's hair was clearly going to be portrayed as great.
Penny Marshall and Cindy Williams started working together as writing partners, then Rob Reiner cast them for an episode of Happy Days (Cindy was also an ex-girlfriend of Henry Winkler at that point) and the rest is history, as Laverne and Shirley were such popular characters they got their own show...until Cindy Williams quit in 1982 because she was pregnant and they wanted her to work right up until her due date. That left Penny to finish out the show solo for the rest of that season, and then it ended.
Anyway, a career synopsis is the best I can offer - Penny Marshall kept out of the spotlight for the most part, which in a way is the most refreshing part about her given the way most celebrities are these days. I have to say she always reminded me of my mother's younger sister somehow (even though Penny was easily 20 years older). R.I.P.