Judging by the shape of the upper sleeves it looks like it is a photo of someone taken in the early 1890's. There's also a quantity of machine-made lace on the bodice that is more 1890's than late 1880's.
So, for me, sorry, nice try but no cigar to the person who tweeted it.
I am not an expert on Victorian fashions, but I do know a bit from years of attempting to date family history photos.
The sleeves appear to be the popular "leg o' mutton" style, which came into fashion in the early 1890s.
Even if this is a very early example of this style, I doubt that someone of Mary Ann Nichol's social status could have afforded to buy such a fashionable piece of clothing until second hand examples became available, ie a good few years into the trend.
I therefore am pretty sure this image could not have been taken in or before 1888.
Just some general comments. The lady seems to be standing near a shelf with a cup on it. Could this be in a pub? And she seems to have the trace of a double chin. Was Mary Ann Nichols fat or chubby? It's nice that the lady seems to be smiling here. She may have been in a good mood when this picture was taken. It is certainly not a studio picture as that required patience with the photographic artist setting up the pose.
Historic clothing is kinda my thing and this image is definitely NOT from the 1880's. As was previously noted, that style of sleeve was not popular until about 5 years after the murders and given that this does not appear to be a high fashion person, it is probably from later in the 1890's rather than earlier. That style of sleeve was worn well into the early 1900's, not really disappearing until 1910 or so.