The EC you describe is awesome. And glad she cared for her sister that much to learn ASL.
I think it will say a lot about her and her values. Those values are very important.
But it is not a hook as they described in what you read.
Hooks get your application to be considered in a different pile.
This includes athletics for a sport in which they need and want you. Certain ethnic backgrounds and geographic diversity to balance a class. Donor development at the highest levels. First generation college. Legacies. High profile celebrities and politicians. Prodigies in the arts as well. Employees and professors of a school also can also give you the extra look while being reviewed.
However. Here is the really good news.
There is life beyond the ivies. Schools with brands nearly as selective and prestigious. Not that it really matters in the end, but foolish to say it doesn’t exist.
And schools that would be equally good at educating your daughter. Schools that perhaps would really connect with her EC and application.
If she likes the east coast. Think of the top flagships in the east UVA UNC GTech and Midwest like Michigan. Really any state flagship in the east and NE would be great.
East coast/mid atlantic private schools like Duke NYU Georgetown (who seem to love quirky language ECs) and Emory. in Boston you have Boston College BU NEU.
Not to leave out the Chicago schools like UChicago and Northwestern that have the same type of environment as the traditonal east coast schools.
And so many liberal arts colleges in the east and New England. Just to name a few. Tufts Williams Amherst Wellesley Vassar Swathmore Bowdoin Wesleyan Smith Colgate. This is just the tip of the iceberg.
And some of these schools will love the ASL EC snd backstory.
Coupled with a statistically powerful application and well written essays. Teacher recs. Course rigor. The entire package is looked at and considered as the full picture.
Good luck and sounds like a wonderful child you have there.