First of all, let's look at the first aspect: the physical state. The Knight of Swords refers to a person who has the strength and courage to face difficult situations. This card seems to indicate that even though the sister has gone through a difficult time, she is strong enough to overcome it and recover.
The second aspect, i.e. the emotional state, is represented by the Empress on the obverse. This card symbolizes unconditional love, caring, acceptance and generosity. It seems that her sister has strong emotions towards her ex boyfriend and they can be reconciled.
The last aspect, i.e. the spiritual state, is represented by the Two of Cups. This card is a sign of inner peace and emotional harmony. There is a sense of mutual acceptance between the sister and her ex-boyfriend, both have learned important lessons from past mistakes and have reconnected with a new positive attitude.
Based on the information obtained from the Tarot cards, there seems to be a good chance that the sister and her ex-boyfriend could get back together. The cards suggest that they both have an inner strength to overcome difficulties and that there is a strong feeling between them that can lead to a reconciliation. Therefore, the most likely answer to the question is, "Yes, your sister and her ex-boyfriend can get back together."