Bede, in 725, wrote that the month Eosturmonath was named for Eostre, a dawn goddess. That single sentence is the entire evidence for her existence. German Ostern matches; every other language calls the feast some form of Pascha, Passover.
Assessment: Documented but thin. The English name rests on one source; the feast's timing rests on the moon.
Stories
Ishtar reborn
A viral claim derives Easter from Ishtar, the Babylonian goddess, citing eggs, rabbits, and fertility as smuggled paganism.
Assessment: Phonetically tempting, geographically and chronologically stranded: Ishtar's name never traveled to Germanic Europe, and eggs and rabbits attach to the feast only in late medieval and modern folk custom. Pagan echoes in spring festivals are broadly real; this specific ancestry is not.
Interesting claims
The goddess kept the calendar
The astrotheology claim: Easter is computed by the moon, the first Sunday after the first full moon after the equinox, because it is a goddess festival in Christian dress, Ishtar, Astarte, Eostre, all Venus under shifting names, and the Council of Nicaea fixed the date to preserve her cult under cover.
Assessment: The lunar computation is documented and genuinely anomalous for a solar-religion feast. The Venus chain is etymologically unsupported beyond Eostre. A case where the scheduling facts are stranger than the theory built on them.
Sources and further reading
Bede, De Temporum Ratione 15, Eosturmonath and the goddess Eostre
Worth asking
Easter is dated by the first full moon after the equinox: the calendar is genuinely astronomical. Does the festival owe more to a goddess, to Passover, or to the moon itself?