I think “drop-off” is probably a poor word. What we really would have to do is look at how women who had arrived before 1990 had done during their recent arrival years. In that sense, we're comparing apples and oranges. The recent arrivals have not really had time to adjust.
On the other hand, while we say their employment and income levels are lower, they're a very well-educated population. Among recent immigrant women, more than one in four has a university degree, so they have some tools to work with. To make a comparison between the two, whether recent immigrant women are currently doing better or worse than their counterparts, you'd have to go back and compare how those women were doing after they had been in the country five or ten years. My guess is you would see a similar pattern.