Need advice on a property owned by my parents and my deceased aunt

Years ago, my father, mother and my aunt,a childless widow, who died in 2004 bought an agricultural property. When my aunt died, my uncle, a childless bachelor, who is the brother of my mother and my aunt gave my aunt's share to my mother verbally. My uncle died last year. Now, one of my cousins who is the daughter of another deceased aunt (the oldest sister of my mother) seems to want to claim the portion of my aunt's property. She is asking for the deed of donation. Since my uncle gave the property verbally to my mother, we do not have the document to present to her.

Question: Does my cousin have the right to claim this property? Does she have the right to ask for a deed of donation to support our claim that the property was already to given to us by our uncle?

I tend to think that it is my mother who is the rightful heir to my aunt's property even if there was no act of giving from my uncle.

Please advise. Thank you.