The sister-in-law seems happy now, but without a man by her side, let alone a child, she's wasting her good youth at the Shen family. When she gets older, she'll have many days of regret. By then, when her children and grandchildren fill the hall, the sister-in-law will be all alone, how miserable.
With the sister-in-law's current behavior, when the third brother returns, he'll surely ignore her. Maybe he'll want to separate as soon as he comes back; she didn't even get a marriage certificate with him.
The third brother has been away for almost half a year; managing to stay away for so long suggests he probably found a way out. Perhaps when he returns, he'll come back splendidly. Don't pay attention to how the mother-in-law usually scolds the third brother harshly, but after all, that's her son. She'll be gratified if he becomes successful and heartbroken if he suffers.
By that time, let's see what the sister-in-law will do.
