Margreet de Heer, who sometimes uses the pseudonym Senoeni, grew up in the North of Holland. In 1990, she moved to Amsterdam, where she studied Theology at the University of Amsterdam. From 1994 until 1996, she was an exchange student in Edinburgh, Scotland. Upon her return to Holland, she started to take her hobby of drawing comics more seriously and joined Maaike Hartjes' comic studio De Zwarte Handel.
Her first self-published comic, 'Misc. I', appeared in 1999, soon followed by 'How To Get Over Your Ex?', which can be read online on her site. Around the same time, Margreet graduated as a theologist. Not feeling that she had a "calling" in the church, however, she decided to look for a job around comics and found one at the comic store Lambiek in Amsterdam, where she worked for five years as a web-designer. In autumn 2002, she started the comic series 'Kinderleed Komix', about her experiences as a stepmother.
In 2003, Margreet founded Senoeni Comics Productions, through which she publishes her own comics, as well as those of children who show a talent and interest in comics. Margreet contributes comics to several magazines, such as 'Isa' to weekly magazine Yes, 'Mijntje' to lesbian magazine Zij aan Zij and 'Stella' to girls' magazine Flo'. She also drew for newspapers NRC.Next and Trouw. Together with Kees Kousemaker, she wrote 'De Wereld van de Nederlandse Strip', a book about Dutch comics, published in 2005. Her comic about western philosophy, 'Filosofie in Beeld', was published by Meinema and presented in Galerie Lambiek in March 2010. The follow-up, 'Religie in Beeld', was published in 2011 and presented in Galerie Lambiek on 25 February 2011.