Black Spot on Female

Question
I have a Russian dwarf hamster (not sure if she is a robo or Campbell).

She gave birth to a litter of 9 and they are all healthy and are one week old now.

I noticed that there is a black spot near one of her lower nipples. It is located at the same level is the vagina, but is shifted towards her left leg. At first, I saw her limbing on the other leg, and thought that her left leg might be broken. The when I offered her some sand to roll in, I noticed that big black spot (the black area has no fur) And it looks there might be another pup that was not delivered and died in the womb, but started to decompose there. Maybe that explains the color. But as for the mother, she is now walking normally, and acting as if nothing is wrong. Although the black spot is still as is.

What could this be?
I tried searching the net about this, but the closest thing I found described a black spot as a gland that hamsters use to mark their Territories. I really doubt that in my female since it looks too obvious for a gland.

Oh yeah, this spot takes place on one of her nipples. No pup is trying to drink from that area. I am not sure if the nipple is damaged or not, because I can't see it. But the other nipple on the opposite side is ok.

Sorry for making this such a long question.
Please help me.

Advanced Thanks and Regards.
Ahmad Al-Mutawa
Riyadh, Saudi Arabia

Answer
It sounds like a nipple that may be bruised or infected. I would really take your dwarf hamster to a vet since it seems that it may be hurting a little bit if she won't walk on that side. I haven't heard of anything like this either, but it does sound like the nipple is bruised or infected in some way.