Much better! Now we can have an actual conversation
A little bit of a background:
The typical AOS process takes years to complete, unlike a DV based AOS which must be completed within the applicable FY. Because the AOS process tends to take take, USCIS provided an opportunity in the form of an EAD card for someone waiting for their AOS petition to work while waiting.
The EAD processing time is typically 3-4 months which is okay for someone with none DV based AOS petition who wishes to work while waiting for an approval. The time frame typically makes it a 'worthless' document for someone with a DV based AOS, unless the person is stuck in background check for months, and they desperately need to work. It may also be useful for a F1 student who wishes to work more hours than currently allowed or whose OPT is coming to an end and wishes to continue working without a break (however there is a caveat to this which I already covered); or for a H/L visa holder who wishes to work for a new employer - since their current work authorization is specific to their current employer.
So:
1. You don't "have" to, that's why the spreadsheet says optional. You may if you like or want.
2. The EAD card start date will be noted on the card when it is received - valid for one year. A GC holder doesn't need an EAD to work.
3. If she likes or wants (you have the story I told above
to guide you on this)