I don't think it was a slap; if you look closely, previous panel shows Jinju fondling Doyeon's breast but when she "saw" her husband instead, she immediately removed her handThis don't quite add up.
Remember when she saw Doyeon sleeping and remembered her husband and the only reaction she had was trying to slap the "memory/image" she saw of him until she snapped out of it and saw it was Doyeon sleeping there.
I think she realized after everything that she hates him
If you go by this context, the "guilty feelings" adds up