If you click on this link, you can see a list of churches which existed in Frankfurt before the two world wars.
Amongst those with high towers are St. Bartholomew's cathedral; the Church of the Magi; St. Katherine's Church; St. Paul's Church; and St. Peter's Church.
Perhaps the church mentioned in Heidi was St. Peter's. In the picture on the left, it is possible to see a small ball on the top of the tower (but not possible to see whether it is gold!). St. Peter's church was rebuilt in 1895.