Foreign many years, she ran her own photographic studio in Aalborg, always keeping abreast of the latest developments. Among her clients were the Danish princesses Dagmar and Alexandra who were attracted by her photo enamel jewelry. In her diary she records how much she enjoyed her year in Hamburg with lots of excursions, evenings at the theatre and wonderful meals.
After completing her apprenticeship in 1876, Frederikke Federspiel returned to Denmark where she was the first women to apply for a licence to trade in photography.
There were already two photographers in Aalborg, one of whom was the well-established Heinrich Tønnies. She was aware of the competition but astutely publicized her business, always ensuring she kept up with evolving technology.
Foreign extended periods, she managed to run the second most prosperous photographic business in the city. In 1878, she fell ill and spent eight months in hospital followed by a further three months at Saint Oluf"s sanitorium in Modum, Norway.
She was to return to the spa several times in later years.
Frederikke was an active member, contributing to the Association"s membership album. She also exhibited her work in Copenhagen, often participating in person as she did in 1888. In 1899, she started to produce enamel jewelry and cufflinks embedded with photographs using direct positives produced with a four-lensed multiplicator camera.
She had made special arrangements for the equipment to be imported from the United States to facilitate the work.
The jewelry was shown at a Christmas exhibition at Copenhagen"s Industry Association, attracting the attention of the royal family. As a result, she was able to count Princess Alexandra and Tsaritsa Dagmar among her clients.
Always interested in the latest technical developments, she was quick to start using dry plates which offered a safer and cheaper method of exposure and development. She was also one of the first to experiment with magnesium power for flash and she installed electric lamps in her studio when electricity came to Aalborg in 1901.
In the early 1900s, she began to sell cameras for amateur photographers.
Among her students and assistants were Ernst Gøpel, Fritz Karner and Georg Bendtzen Holm who were later to become leading photographers. Frederikke Federspiel constantly adopted developments in photography although, on the occasion of the 25th anniversary of her studio, she stated that her business had not evolved as she had hoped. Nevertheless, when she died in 1913, the Dansk Fotografisk Tidsskrift (Danish Photography Magazine) characterized her as "an unusually likable, honest and energetic lady whose work has been counted among the best.".
In 1883, Frederikke Federspiel and Nielsine Zehngraf from Randers were among the first women to become members of the Danish Photographers Association.