I watched replays of her Wimbledon QF and SF matches, and I have to say I'm impressed.
1. Forehand is her best shot. It's not just powerful, but she can open up both sides of the court with the angled forehand.
2. Return-of-serve is nicely aggressive, and she blasted several outright winners in just the two matches I saw.
3. Serve is decent and can get even better. It's not overwhelmingly powerful, but has good placement.
4. Backhand is her "weaker" side, but still very good. Her backhand down-the-line was working well against Bencic. Her cross-court backhand is more of a rally shot, so she should be looking to run around it and create more with her forehand. The defensive slice backhand needs some work (usually set up an opponent's winner).
5. She did some good defensive scrambling and can probably use her athleticism even more, like her coach said. If she is looking to be aggressive and move forward, she can really do some damage.
Overall, I like what I see and there's a lot to expect from her in the future!
And to think her best surface could be red clay - that's almost shocking for an American.