I suppose you could state she was half Swedish since her mother was from a Swedish family from Stockholm.
Tove was surely gravely insulted when somebody called her Swede. Especially after Winter War. Finland and Sweden had defense pact but Sweden choose to be neutral and promote peace. And so it deliberately hindered war effort preventing arms transport from Norway ports. Only aid was volunteers, which were mostly Finns living in Sweden.
Grok:
Tove Jansson was a Swedish-speaking Finn, not half-Swedish. She was born in Helsinki, Finland, in 1914 to Finnish parents, Viktor Jansson and Signe Hammarsten-Jansson, both of whom were part of Finland's Swedish-speaking minority. This community, known as Finland-Swedes, speaks Swedish as their native language while being culturally and nationally Finnish. Tove's mother was born in Sweden but moved to Finland, which might cause confusion, but Tove herself identified fully as a Finnish citizen and a member of the Swedish-speaking Finnish community. Her works, like the Moomins, were originally written in Swedish, reflecting her linguistic and cultural background.