If a pregnant lady was unable to keep fasts in the month of Ramadan due to the pregnancy, she has just to perform the qada and there is NO Kaffarah for this.
However, the fidya is obligatory if the qada was not observed within one year without any legitimate reason. Yes, if she was not able to keep the qada due to child feeding etc, then there is no fidya as well.
NOTE: Fidya is a compensation of not fasting due to valid reason. The fidya is 750 grams of grains or an equivalent amount of it. Plz refer to this for more details: