My friend and I were playing using the Capital City. When I played it, I saw three choices: 2 cards for 2 coins, 2 coins for 2 cards, or "Don't". She saw only one choice: 2 cards for 2 coins and then the other choice IF she did that one. Why? What can she do to see the proper choices?
At the time you played Capital City, you already had generated $2 (= 2 coins) or more (say from playing Militia or some other Action cards that give you coins earlier that turn). That means you can spend those 2 coins and draw 2 cards and then go on with your turn.
Your friend however did not have $2 at that time. That means the option to spend $2 was not initially available to them, so it isn't shown. Once they discarded 2 cards for the other option, they did have the $2, so the option was shown to them.
On the card, after giving you +1 Card and +2 Actions, you have 2 independent parts that are both optional. You may first discard 2 cards to get +$2. Afterwards (if you did that or not), you may spend $2 to get +2 Cards.
So formally you would have to decide, after getting +1 Card and +2 Actions, if you want to use the "discard 2 cards to get +$2" effect. Only once you made that decisions and executed the effect if you chose to, would you decide upon using the "spend $2 to get +2 Cards" effect.
In order to remove unnecessary clicks in the game, the user interface presents you with all the options you can actually do at the time. So if you have 2 or more cards in hand, it will show the "Discard 2 for +$2" button, if you have $2 or more coins already, it will show the "$2 for +2 Cards" button.
The understanding is that the player can then choose the first option they actually want to use, without being bogged down by explicite questions if to use this or that option. All the currently available options are shown, then (if chosen) the option is executed, then again all available options are shown (which may be different now),