This was tricky to translate because of the many multiple meanings of お慕い and 命, and unlike typical uses of the words, (nearly) all the meanings are intended, so I have to juggle a bit by picking one primary word and then 'coloring' it by adding a few more as support. Hopefully I managed to get the sheer emotion of the scene (and the resonance in multiple meanings) across.
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命 in particular can mean "life" (i.e. the vital force or act of living), "lifespan" (period of living), "important things" (one of the 命 above is given the alternate reading "everything" to emphasize this particular meaning), "fate", and "decree". All these meanings are intended, though the primary one here is "life".
Updated
Sister...
Even if "this" were your will,
I cannot accept it—!No matter how painful it may be...
If it is your fate to come to an end, then that—I can accept.
I've always admired you—adored you—from the very bottom of my heart.
I love you, dearest Sister, your life,
your everything!