Irish has very colourful expressions for dying. To lose one's life. To meet death. We do say these in English too, the first one anyway, although I think of that being used more in reference an accidental death or a violent death through war or whatever, rather than a "natural" one. Does this have the same sort of intent in Irish, or is it a common way to say that someone has died?
I searched on Google for both "chaill é a shaol" and "chaill sí a saol" and got little to show for it.
Searching Pota Focla for "lose life" gave three results, all using "beatha" to mean "life"; foclóir,ie has this one example under "life":
"he lost his life - fuair sé bás, bhásaigh sé, cailleadh é, d'éag sé"
with "saol" not appearing in any off the given alternatives.
"saol" seems to refer more to the period of life (lifetime), way/condition of life (lifestyle), achievements or experiences, whereas "beatha" is the state of being alive or "the fact of being alive", as Pota Focal notes under "beatha".
But even using "beatha",and variants, with various forms of "caill" didn't turn up many results.
I was given, as the "correct answer", "Her grandma lost her life ". Why "grandma" for "grandmother"? (I note that the answer given at the top of this page is "grandmother").
"her grandmother died" - fuair a seanmháthair bás
"her grandmother lost her life" - chaill a seanmháthair a saol
The two different idioms exist for a reason - there are circumstances in which one is more appropriate than the other. If you want to impoverish your language by only learning one of the idioms, go ahead, but Duolingo wouldn't be doing you, or any other learners, any favours by encouraging you.