EXCHANGE INTERFACE

After Peggy Carter and Natasha Romanoff, Maria Hill is now the female character who's had the most on-screen interaction with Steve. And maintains a very friendly-comfortable relationship if Steve's (paraphrased) comment of "Allowing a mad scientist to experiment on their body? Who even does that?" is any indication.

For canon? A marginal and unimportant detail.

For fandom? That's pretty big. :)