Note: I'll keep longer list than normal here, and will add cards frequently when good suggestions are made. I also will not keep a list of rejected cards, since I want to keep an open mind as consensus around the best ways to play Giada form.
1) Avacyn, Angel of Hope
This card absolutely belongs in an angels tribal deck yet, and this one is no exception! Big flyers are board-wipe bait, and with Avacyn we can rest easy. The only reason she is not in is that I haven't bought it yet because she is expensive. I sell off stuff for store credit periodically and get magic money for birthdays and such, so one day she will definitely go in!
2) Archangel of Tithes
This is another great angel with good abilities. I'm not sure she's strictly necessary since deterring blockers isn't a huge deal when your deck is full of flyers, and I'm not sure I'll need the mini Ghostly Prison effect, but she is on the list. I think the biggest upside to her is that she shuts off infinite attack step and attacker combos like Godo/Helm and many others because the tax keeps them from working. Sometimes these corner cases is the difference between a win and a loss.The only reason I haven't tried her is because she's not cheap, and I'm not ready to invest in her quite yet, but likely will.
3) Esper Sentinel
This is a great one-mana draw piece. We don't have a lot of synergy with it since we don't have a lot of ways to put counters on it, and competitive opponents will pay the tax. It is also worth noting that it only triggers on the first non-creature spell each turn, so it's not Rhystic Study by any means. Still, it will likely draw some cards over the course of the game, is super efficient, is a one drop (which this deck loves), and even if it only draws a single card the cmc is probably worth it, and in most cases it will draw a few. It definitely belongs in the deck, but I haven't pulled the trigger yet because of cost.
4) Armageddon
This is a controversial card, and some of you might overlook it for just that reason, or because you know the social contract in your meta will punish you. Still, I think personally that it's a fair card in a mono-white EDH deck, and that it is probably correct to play it here. This deck is very fast, but blue and green already have such an advantage in ramp and draw that they can outvalue white if given time. Our main goal is to kill those players first, but often times if we can just reset those other advantages we can win. Because of our curve we can always rebuild our mana base fast, and we'll often start out with the best board state. This card helps hold our opponents down till we can finish the job. It also has an appropriate theme to an angel deck, and combos brutally with Cosmic Intervention if we really want to put them back. I more than understand if people don't want to play it on principle, and I may or may not myself, but I am thinking it is the correct play.
5) Serra Ascendant
He's not an angel, but the turn one flying life-linker is real and can power our life-gain engines. It's a must remove, but it will rarely be efficient to do so. I'm not sure about it though, and the price is also real, but I have my eye on it.
6) Victory's Herald
Lifelink aura is one of the best things you can do in this deck, so why not another way? The main objections to this so far relate to raising the cmc too much for another six drop and what to cut for it, as well as the fact that unlike Lyra Dawnbringer and Angelic Skirmisher it has to survive a turn around the table before we use it, but it's a good option.
7) Angelic Arbiter
One of the more experienced and active Giada players on Reddit has recommended this card, and I do have to concede that it could be a strong entry into the deck, with the ability to slow down our opponents a ton. I am thinking about it, though I do find that usually most players aren't in much of a position to make good attacks against me and it is high cmc, so I'm undecided.
8) Luminarch Ascension Update
I'm not quite sure why this missed the first draft, because it comes down so early and easily allows us to place tokens in a burst. Of course, it could get blown up before it does anything, but it seems like one of the few angel token generators besides the life-gain based ones that could be really good here. If I were to put it in, it would probably replace Starnheim Unleashed since it is a mana sink that's a bit in the hail mary category of cards.
9) Pyre of Heroes + Breathkeeper Seraph NEW
This combo is well established in the Giada community. Pyre is a great tribal tutor that allows us to sac an angel to bring an angel from our library onto the battlefield, and Breathkeeper Seraph makes it a tutoring draw engine, since we will always get whatever we sacrificed back on our end step. We can even sac the Seraph to tutor out Sephara, Sky's Blade, which is definitely the ceiling of this combo! That being said, I have a lot of experience with Pyre of Heroes, and on its own it is nowhere near as good here as it is in toolbox decks where it is overpowering. There are definitely cases where we will be happy to trade a three drop for Linvala, Keeper of Silence or Angel of Jubilation (even though the latter turns Pyre off). And if we have out a recursion piece we may not even feel the sacrifice too much. That being said, I am unsure whether trading one angel for another will be as good here as elsewhere. With Breathkeeper Seraph we do have a piece that can protect our best creatures including our commander, and we certainly would love it in tandem with Sephara, Sky's Blade. While six drop angels function as five drops in this deck due to Giada, we still want to be careful not to have too many pieces at this high of a cmc. It is also worth mentioning something about tutoring here. Combos like this are strongest when we have tutors for them. Changing Steelshaper's Gift for Enlightened Tutor can get us the Pyre, but the only way to tutor Breathkeeper Seraph in white is with the Pyre itself, which requires a five drop to sac to get us there. All this means is that this combo won't happen as often as we'd like it to, so if we include it we need to consider the pieces worth it on their own. With all of that said, I am very seriously considering this combo and would be curious to hear the experiences of those who have tested it.