There is nothing in Genesis 3:15 or the surrounding context to indicate the sin of the garden involved sexual relations between Eve and the serpent.

counter-argument of

Styrax japonicus (Wikipedia) Styrax japonicus (野茉莉, also エゴノキ, egonoki), also known as the Japanese snowbell, is a species of flowering plant in the family Styracaceae, native to Korea, Japan, and Southern China. Growing to 12 m (39 ft) tall by 8 m (26 ft) broad, it is a graceful, spreading deciduous tree with oval, upward-facing leaves which occasionally turn yellow or orange before falling in autumn. Masses of slightly fragrant, bell-shaped white flowers hang from the branches in summer, followed by fruits (drupes) which resemble olives in both shape and colour.

Did Eve Have Sex with Satan? The Serpent Seed View of Genesis 3:15 (equip.org) Branham (1909–65), a proponent of Oneness theology, taught the so-called serpent seed interpretation of Genesis 3, with adherents of this view often citing Genesis 3:15 in support of their position: “And I will put enmity between you [the serpent] and the woman, and between your offspring and hers; he will crush your head, and you will strike his heel” (ESV).