Maria Isabel Wittenhall (sometimes written as Witenhall or Wettenhall) was born in Avintes, in the municipality of Vila Nova de Gaia in Portugal on 6 November 1749 to English emigrant parents.

[1][2] On 4 May 1767, at the age of 17, she married Pedro van Zeller (1746-1802), who came from a Dutch Catholic family and served as the Russian Consul in Porto.

The Royal Family of Portugal experienced first-hand the results of a failure to inoculate when José, Prince of Brazil died of smallpox at the age of 27 in 1788.

[3][2] Towards the end of the 18th century, the work of Edward Jenner and others showed that cowpox delivered by vaccination to humans could protect against smallpox.

The Institute awarded her a gold medal in 1813, although this was subject to some controversy because members thought that another woman, Angela Tamagnini, also deserved such a distinction.