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Ultra-faint dwarf galaxies (UFDs) are commonly found in close proximity tothe Milky Way and other massive spiral galaxies. As such, their projectedstellar ellipticity and extended light distributions are often thought to oweto tidal forces. In this paper, we study the projected stellar ellipticitiesand faint stellar outskirts of tidally isolated ultra-faints drawn from the'Engineering Dwarfs at Galaxy Formation's Edge' (EDGE) cosmological simulationsuite. Despite their tidal isolation, our simulated dwarfs exhibit a wide rangeof projected ellipticities ($0.03 < \varepsilon < 0.85$), with many possessinganisotropic extended stellar haloes that mimic tidal tails, but owe instead tolate-time accretion of lower mass companions. Furthermore, we find a strongcausal relationship between ellipticity and formation time of an UFD, which isrobust to a wide variation in the feedback model. We show that the distributionof projected ellipticities in our suite of simulated EDGE dwarfs matches wellwith that of 21 Local Group dwarf galaxies. Given the ellipticity in EDGEarises from an ex-situ accretion origin, the agreement in shape indicates theellipticities of some observed dwarfs may also originate from a similarnon-tidal scenario. The orbital parameters of these observed dwarfs furthersupport that they are not currently tidally disrupting. If the baryonic contentin these galaxies is still tidally intact, then the same may be true for theirdark matter content, making these galaxies in our Local Group pristinelaboratories for testing dark matter and galaxy formation models.

EDGE: The direct link between mass growth history and the extended stellar haloes of the faintest dwarf galaxies