The only free and comprehensive online etymological dictionary of the Spanish language
ella f. (Pronoun) "she," "her"
From Vulgar Latin illa 'id.,' from Latin illa "that one." From Proto-Italic *olna 'id.' From Proto-Indo-European *h2ol-na- "that." From the root *h2el- "that." See also la.
Indo-European
Romance
Asturian ella, Portuguese ela, Galician ela, Catalan ella, French ella, Italian ella, Aromanian ea, Romanian ea
Italic
Oscan úlleís "of that," Umbrian ullu "toward that"
Celtic
Gaulish ollo- "beyond," Old Irish ol 'id.,' Middle Welsh ol "according to"
Balto-Slavic
Old Church Slavonic lani "last year," Czech loni 'id.'