Fischer has published extensively in the area of English historical linguistics, especially historical syntax, where her interests in syntactic change relate to changes in word order, comparison with developments in other West Germanic languages, grammaticalization, and the interaction between grammaticalization and iconicity in language change.

She holds an M. A. in the History of English and General Linguistics from Newcastle University (1975) and an M. A.

(doctoraalexamen) in English Language and Literature from the University of Amsterdam (1976, cum laude).

She obtained her PhD from the University of Amsterdam (1990, cum laude) with a thesis entitled Syntactic Change and Causation: Developments in Infinitival Constructions in English.

She has also been concerned with the ontological status of grammaticalization, and whether it should be regarded as an epiphenomenon or a separate mechanism in language change.