It's important to note that "cousine" is the French word for "cousin". It's possible you are looking for the Marathi word for "cousin", which is:
* मावशीचा मुलगा/मुलगी (maavsheecha mulga/mulgi) - for a cousin from your mother's sister
* मामाचा मुलगा/मुलगी (mamaacha mulga/mulgi) - for a cousin from your mother's brother
* काकाचा मुलगा/मुलगी (kakaacha mulga/mulgi) - for a cousin from your father's brother
* आत्याचा मुलगा/मुलगी (aatyacha mulga/mulgi) - for a cousin from your father's sister
The specific word would depend on the relationship between you and the cousin.