Artifacts 1 and 2 synergize very well with Estela's kit and will keep you topped off with an overshield in most content.
There's a lot of debate between Resonating and Responsive Pact, but honestly just be aware of whichever you're using and play accordingly.
Furies III and Scorched Earth are generally considered better DPS, but Gallows allows Spread Shinka coverage.
I strongly recommend getting her to T1 if you can; she becomes much more tanky and can withstand a lot more content without thinking.