Oof. Not a good looking foot, but there's no open wound, and it's not purple/black/green, so it could definitely be worse. With no open wound, the neosporin won't be doing much. I'd try to keep her from putting any impact on that foot, by removing any climbing toys, wheels, etc, leaving her with just a short house (small cardboard boxes or even just a cardboard tube). You'll just have to watch that foot in case it does turn colors or a wound opens up.
As for being pregnant, either she'll have pups within three weeks of purchase, or she isn't pregnant. Is she living alone now? You'll want to keep her housed alone, so that the other mice don't eat her pups. If you need access to the culling forum in order to learn more about culling practices, asking a mod is the way to go for that.
Oh I know about the pregnancy part I have raised litters its just killing me not knowing. She is in a 10 gallon and is not interested in moving, I gave her toilet paper for a nest and she just sleeps all day and I check the foot daily. She is currently with two other mice but once I confirm pregnancy she will be moved into another tank ... I am actually ordering them a bigger cage next week.
I will not be culling, Any females will stay with me and I will find non breeding homes for the males. Of course homes that will also not house them together. As long as they are not going into breeding lines I do not think I need to cull.
My mouse with a arm like that but worse. Had it for about a week she is gettin better not worse. She is in a small cage with lots of soft bedding and she barely has room to run around so she doesn't use her arm she was originally walking and holding it up but she can now use t and she climbs with it
Sorry for late reply been busy with new mousery or rather old caravan converted into mousery.
The pics to me look as though the mouse has been standing in either high acid or high alkaline based cleaning fluid due to the blisters on the foot, which also would account for the mouse breathing as either would also cause blisters to the poor animals windpipe and possibly lungs also. A secondary infection would also result from such injury pretty quickly and would require antibiotics to keep that from causing additional problems. The condition of the foot on your first pic indicates to me that the foot had been on such matter for some time and gone un noticed and breathing in of the cleaning agent fumes also would more than likely caused irrepairable damage.
So many pet stores in such a rush with cleaning of cages and hire inexperienced staff that an oversight of not doing the cleaning properly and removing the strong cleaning agent I suspect in this case to be bleach can have such drastic result and suffering of the animals.
Sorry to hear of the loss and good to hear you tried everything you could to ease the animals suffering