How to set Windows bootloader as default bootloader?

Edit that file, from terminal run

 sudo gedit /etc/default/grub 

(file has comments to help you). Find that line and set Windows number (number of Windows line in Grub, starting from 0). In my case that will be

GRUB_DEFAULT=2

Then save file and close gedit. Run that command to update grub:

sudo update-grub 

There is a programm for windows called easy bcd. Install it when running windows and the proceed a described in the following link:

how to use easy bcd

Nevertheless I think also the other answers are valid as the question was basically how to avoid that the sister is scared by grub to choose windows if necessary.

PART 1:

Make Windows (ANY variant) the default Grub2 menu option.

Description: This sets Windows as the default boot option, and (with NO user action) the PC will auto-launch Windows on startup.

STEPS:

A. List your current menu items

sudo update-grub 

B. Edit setup file

sudo gedit /etc/default/grub 

Set the boot default to your Windows boot partition (eg.)

GRUB_DEFAULT=”Windows 7 (loader) on /dev/sda1″

WARNING: Just setting 'GRUB_DEFAULT=n', will NOT work after kernel updates, etc.

(Save the file and close.)

C. Update grub settings

sudo update-grub 

Now, on boot, you will AUTOMATICALLY default to MS Windows.

PART 2: (Optional Extra)

Hide the Grub2 menu, and use the default menu option.

Description: This both hides the startup menu, and shortens the (usually 10 second) timeout. The PC will auto-launch whatever the default option is on startup.

NOTE: The user just needs to hold down the Shift key (on startup), to again see the Grub2 menu.

STEPS:

D. Edit setup file

sudo gedit /etc/default/grub 

Uncomment the line '#GRUB_HIDDEN_TIMEOUT=0', to look like:

GRUB_HIDDEN_TIMEOUT=0

(Save the file and close.)

E. Update grub settings

sudo update-grub 

Now, on boot, you will AUTOMATICALLY boot to the default menu option, UNLESS you hold down the Shift-key at boot time. Then the grub2 menu will re-appear.

FURTHER DOCUMENTATION:

http://ubuntuforums.org/showthread.php?t=1195275