Here are the siblings and their apparent mother in the 1885 Copenhagen census.
Johanne is listed as married and born in Sweden, but no husband is listed.
In 1860s Gothersgade was listed in Helligands, Trinitatis, and Skt Paul parishes. I searched for Gerda in those records and did not find her, but those more skilled in Copenhagen searches can probably locate them:
København, København (Staden), Gothersgade (ulige numre), Nørrevold Kvarter, , Gothersgade 145,Matr.150 & Rømersgade 25 5.Sal, 12, FT-1885
Name: Age: Marital status: Occupation in household: Occupation: Birth place:
Johanne Rasmussen 37 Gift Husmoder Dameskræderinde Sverrig
Gerda Edit Rasmussen 8 Ugift Barn Kjøbenhavn
Josepha Marie Rasmussen 10 Ugift Barn Kjøbenhavn
Octave Ansgarius Rasmussen 2 Ugift Barn Kjøbenhavn
Charlotte Mariane Petersen 20 Ugift logerende Syerske Tyskland