What resolution is your image? The physical size (12 x 14) and the resolution are two different things. It sounds to me like you probably used screen resolution—72 dpi (dots per inch)—rather than print resolution, which is usually 300 dpi but can be less depending on the printer's requirements and method of print production.
If this is the case, there isn't much you can do other than RECREATE the original at the correct dpi. Don't try upsizing the dpi, you will end up with a badly pixelated image.
To check your image size and pixel resolution, open the image and go to Image>Image size. In the middle of the dialog box you will see the size listed, the bottom box in the section is Resolution. That will tell you if the problem is resolution being too low.
Note that if you sent the image via e-mail, it would have been hard to send a 12 x 14 image at 300 dpi; that's a huge file. You don't say how you sent the image.
If this is the case, there isn't much you can do other than RECREATE the original at the correct dpi. Don't try upsizing the dpi, you will end up with a badly pixelated image.
To check your image size and pixel resolution, open the image and go to Image>Image size. In the middle of the dialog box you will see the size listed, the bottom box in the section is Resolution. That will tell you if the problem is resolution being too low.
Note that if you sent the image via e-mail, it would have been hard to send a 12 x 14 image at 300 dpi; that's a huge file. You don't say how you sent the image.