Person A is reminiscing and beating herself over her supposed failures at not saving some people including B who had to go away.
Bさんの時もそうだった…
もっと強くもっと早くこの手を伸ばせていれば
ようやく巡り合えた愛しい相手を残し瞳の奥に涙して笑顔で空に還ることも
母のように娘のように大切にしていた相手を見送るしかない強く哀しい選択も
させずに…すんだはず
This is the provisional translation without the end bit which I don't get.
That also happened with B-san...
If I had reached out with this hand of mine more quickly more strongly...
1: Finally being able to meet the one you held dear and return to the skies with a smiling face while concealing tears in the depth of your eye...
2: And also the really sad choice of having no option but to part with a person you cherished like a mother, like a daughter…
???
Given the context, I'm assuming the entire thing is basically an elaborate "If I tried harder the bad things 1 and 2 wouldn't have happened", but I don't really get how させずに…すんだはず works or what it means.
I do get that すんだ = するのだ and that させずに is kinda an adverb (?) meaning that without doing something A expects something happens? But yeah, I don't get this part at all really.
I guess the question would be what does this part mean, and how would one translate it?