How many people do you need to seat at your dining table? You don't want an overcrowded room.

48" seats 6

36" seats 4

You need a minimum of 2 feet of clear space to pull out chairs entering and exiting the table.

IMO 2 ‘ is not enough space around a table I like 3’ and IMO you do not have enough space for any but a very shallow table on one wall and 48” will be good.

Listen to your mother ; )

From your floorplan, I am assuming that the sofa will be moved to the other side of the room. I would stick with the 48" table (round shape is a good plan). I feel a smaller one looks more like a bistro table and doesn't seat 4 easily. However, I would not include the bench below the window and doesn't serve much purpose. I like the utility of the shallow cabinet in the dining area, as long as it is a buffet rather than a tall cabinet which I think would overwhelm the space.

IMO a 36” table will look like a kitchen table not DR

What is the area size? Width X Lenght of the room? Any furniture along the walls? If you draw a small plan and specify the dimensions of the area and indicate the size and location of the furniture in the room, it would be easier to determine the right table size.

Just take that first plan you posted and write down all the dimensions on it or you [Follow This Link[(https://www.houzz.com/discussions/what-size-dining-tables-work-well-in-a-12x12-dining-room-round-recta-dsvw-vd~921263), maybe you can find a similar size dining room size and layout there that matches what you have.

Good luck