If OP applies Yale SCEA, OP would be precluded from applying early to another private institution EA or ED. Given her financial position, ED is not a great option. She may want to apply EA to a less selective school if she wants a better shot of knowing she is in somewhere before Xmas. She can always apply rolling admissions anywhere that offers that or non-binding EA to any public university. I would recommend applying rolling or early to a public both to secure a school and to have a better chance at aid, need and merit.
SCEA (at HYPS) does not prevent her from applying RD anywhere else. If she is accepted, she will not have to commit to attending until May after she has received notice of admissions and aid from all schools that have accepted her. In that respect SCEA does not limit options. If she is deferred, she just moves into the RD pool. If rejected, she can move on. The other Ivies, if she is considering those, are ED and she would be bound if accepted.
OP, don’t apply SCEA if you don’t think your app will be in optimal shape by the deadline. If you won’t have your next ACT in hand by Nov 1 and you think you will do better, apply RD. If you think you need more time to polish your app, also apply RD. If however the app is going to be as good as it can get by Nov 1, SCEA may be the way to go, and not just because of a possible bump. If you get in, it will save a bunch of work and fees in not having to apply to a bunch of other schools RD – just the ones that you might choose over Yale. If you get rejected, it will tell you how competitive your app is and you may need to lower your sights a tad. If you are deferred, there is no harm. Finally, there is 0 difference in aid between SCEA and RD. The need calculation will be the same, and since SCEA does not bind you, you can compare FA offers from all the schools that accept you and perhaps use them against each other to get a better deal.