Depending on the occupation of the father, it is possible for the children to be born different location.
So than this Klara and Franciszek SROKAs are only coincidently named same as your ancestor.
Klara's arrival manifest could be under badly transcribed surname or she could have come under someone elses name if that person could not make it on that date. So many possibilities why you are not finding her arrival manifest. Could she have come thru Canada?