I have a female dog that is about 7 years old she is a mutt, but I noticed that one of her
Nipples has a lump on it, she is not fixed and about two months ago she had a false pregnancy where she carried her stuffed animmal with her where ever she went.
What could it be ?

Likely it is a tumor of some sort. May or may not be dangerous. There is a good chance now the money you saved on not spaying her will go for treating cancers she might not have had.

malaki, instead of asking us to speculate what it might or might not be, bring your dog into the vet, NOW. To wait and think that we may be able to diagnose this online is ridiculous. To let that poor thing go through a false pregnancy is cruel. Hope and pray that it isn't cancer. AND, if it isn't and she is okay, spay her for the sake of her health, both mental and physical.

If she went through a false pregnancy recently, it is a strong possibility she could develop pyometra-a pus filled uterus that has to be surgically removed in an emergency fashion with high risks involved. Talk about expensive and hard on you dog-whew! Set up an appointment to have her spayed immediately as well as removal of said lump for a biopsy if the vet feels that is necessary. The mammary chain of an intact female that develops "lumps" are indicative of breast cancer most of the time.