The last stop on the WMATA Red Line is Glenmont, not "Washington Center".
There is no WMATA station called "Washington Center".
When Aaron first calls Olivia to know where she is, she said had to take care of a few things. Aaron wouldn't have to call because secret service monitors and logs of individuals entering and existing the White House. He could simply check the logs to see Olivia left by herself. Someone as seasoned in secret service procedures should know this.