Jake would not countenance Janis's marrying while still a student.
Is that sentence above omitted from the one below?
Jake would not countenance that Janis is marrying while still a student.

If so, the sentence, Janis is marrying, is like Janis is going to marry if technically not the same, isn't it?

Question

Jake would not countenance Janis's marrying while still a student.
Is that sentence above omitted from the one below?
Jake would not countenance that Janis is marrying while still a student.

If so, the sentence, Janis is marrying, is like Janis is going to marry if technically not the same, isn't it?

Answer

No, "Janice's" is the possessive, not a contraction of "Janice is". "Marrying" is a gerund and functions as a noun in this sentence.