Is there any evidence of the Ancient Greeks worshipping Zeus's daughter Helen? For example, did they build any shrines in her honor or did they offer sacrifices to her?
We first a crown of low-growing lotus
having woven will place it on a shady plane-tree.
First from a silver oil-flask soft oil
drawing we will let it drip beneath the shady plane-tree.
Letters will be carved in the bark, so that someone passing by
may read in Doric: "Reverence me. I am Helen's tree."
Theocritus' epithalamium commemorating the marriage of Helen and Menelaus
Helen was worshipped and had a festival at Therapnae in Laconia; she also had a temple at Rhodes, where she was worshipped as Helen Dendritis (Helen of the Trees, Έλένα Δενδρῖτις); she was a vegetation or a fertility goddess(the tree goddess).
Like her brothers, the Dioscuri, she was a patron deity of sailors. Her name is pre-Hellenic and the cult may go back to the pre-Greek periods.
Herodotus, in his Histories, recounts the story of how Ariston took his third wife, the most beautiful woman in Sparta, from his friend Agetus, and says that she had been an ugly baby, but her nurse's constant prayers at Helen's shrine had caused Helen to appear and make her beautiful.
If the story is not accurate, nevertheless the existence of the shrine is very likely.