It sounds like you are considering construction lumber for the table top. Not the best material.
This link explains the different grades of construction lumber and the different moisture contents.
KD is max 19% moisture content at the time of milling.
KD-15 is max 15%.
A hardwood lumber mill which kiln dries, may dry to 11-12% depending on how the operator runs the kiln.
Whatever wood you purchase is going to experience moisture change. Typically this will be loosing moisture to get to the same moisture content as your shop and later the room in which the project is placed. Hence it is possible you make the item, it looks fine, then you move it to an air conditioned room, and it "moves" aka, twists, cracks etc. due to the room having even less moisture.
There are many threads on the forum about people having problems making projects from construction lumber.
If your daughter insists on using construction lumber, I would use 2x4 rather than 2x12. It is easier to find straight boards in the "Premium" grades of construction lumber. Some may have waxed ends to reduce cracking, perhaps the KD-15 moisture content.
The narrower boards will crack less, and if one decides to crack or twist, it will be easier and less expensive to replace.
As others have commented, planing does not stabilize the wood. If I am using construction lumber, I may plane it to get a smoother surface or remove scratches/chips from the mill. Perhaps a good idea for a table top. I only take off perhaps 1/64in. A light pass.