I'm fairly certain Tsunade calls her a prodigy at medical jutsus. And the asspull is her having the seal in the first place, there was zero buildup to it, and it was just given to make her look equal to Sasuke and Naruto during the war arc
Well, if medical ninjustu I still wouldn't call her a prodigy. But the seal actually did have a build up. Like I said about putting one and one together.
Jiraya picked up Naruto and taught him most of his stuff.
Orochimaru had his balls set on Sasuke and taught him most of his stuff.
Then Tsunade was introduced. Being that Sakura was the only one out of 3 that wasn't picked up by a Sannin, it was bound to happen. Now, since that was bound to happen, she learned Chakra Enhancement and Yin Seal which is why it shouldn't have been a surprise that she got it.
If Naruto learned most of his jutsus from Jiraya and Sasuke learned most of his jutsus from Orochimaru, it would be reasonable to suspect Sakura of eventually getting a few from Tsunade.
And if you mean where Kishi actually shown you her training and such, I don't think that would have been entertaining. I mean, it's quite obvious that she isn't the most liked character in the story so wasting time to show her get knocked around rather than showing a quick little flash back would be better so they kind of made a smart move there. It's different for Naruto and Sasuke being that they are the essential characters.