Is this a post-mortem photograph?

[USCRx]

This is an ambrotype from 1855-1860 (Canadian). The woman in the photo is my g-g-grandmother, Agnes (Moscrip) Jeffrey (1819-1873). I've been told that this might be a postmortem photo. Would love to hear impressions from some of you in the group about this possibility, and what leads you to your opinion.
Here's as much as I know about the woman. Agnes Moscrip was married in ~ 1839 to a John McLenhan. They had 4 children, born in 1841, 1843, 1845, and 1848. In September 1847, her husband and two sons, aged 4 and 6, all died of dysentery. Her two other children survived. She then remarried my g-g-grandfather, Andrew Jeffrey in 1853, and had 4 children with him, in 1854, 1856, 1860 & 1862. I was told by a ambrotype 'expert' that the photo is mid-1850s at the latest. I've not found anything that mentioned a death of an infant. So that's my dilemma. Thanks for any thoughts you might have!

[River Tyne Lass]

My thoughts are this might be a post mortem photo.  Left arm does not appear in a cradling position as you might expect to see showing when holding a living baby and supporting their head.
There is also a seriousness and sad look to the woman's face.  I know people didn't usually smile on photos back then, but the expression has a look of loss to me.
Added: I agree in your comment on what baby is wearing Erato.

[Erato]

The baby is dressed in what looks like sort of a black shroud.  Surely that kind of clothing wasn't the norm for a living child.

[Treetotal]

The date for the photo is about right for the style of clothing. I would agree with RTS and Erato's comments. The baby is dressed in dark material, presumably black,  and the pose of the baby is unnatural and stiff looking. There is a sadness to the photo.
Carol

[River Tyne Lass]

Also, just to add, zooming in there looks like what might be discolouration setting in on the top of baby's ear.

[Gadget]

I agree with date and  it does look like a pm photo. The child  looks lifeless and the dark clothing  is also suggestive. The  face looks puffed and is held up by mother. Also the arm seems odd. Mother looks sad.


Gadget

[USCRx]

I don't think the baby's dress needs to be considered black. See attached color comparison.

[suey]

I’m no expert but I disagree. The mothers hand can be seen just behind the baby’s shoulder and neck.  Surely with an infant of that age, and the child looks well nourished you would expect to find a death or burial.

[Ruskie]

I also think this could be a PM photo. The child does look well nourished but might that still be possible depending on the cause of death?

Perhaps not black USCRx, but it is unusual to see a baby wearing such dark clothes.

It struck me as odd, (though maybe it is not) that the mother is wearing heavy winter clothing yet the child is not, and her/his arm is uncovered.