Is it legal to transfer deed to family member to reduce down payment on an additional home?

My sister owns a house in Connecticut and a house in South Carolina. She wants to buy a third house in South Carolina, but the down payment will be $30,000 more than she can afford. This down payment is $30,000 higher than she expected because the two South Carolina houses would be within 50 miles of each other. Her idea to reduce the down payment by $30,000 is to transfer the deed of the South Carolina house she already has to my mother's name. My mother would then pay my sister for this house at a later date. Would it be ethical and legal for them to do this? What if my mother decides not to buy house number two from my sister and transfers the deed back to her? If the deed transfer is just temporary, could my sister's mortgage application for the third house be considered fraudulent?