Yes it is possible to merge the two partitions however I would not. I would move "My Documents" and "My photos" to the D drive. This will give your data a measure of protection should you need to re install / recover Windows.
The process is very straight forward. Start Computer Open D Right click and create a new folder Documents, Black Hole, Anything you like....
Go back to Start Click on your wife's name and this will open explorer and show all her folders Right click on My Documents Select Properties, at the bottom of the list Select the Location tab Move Browse to the newly created folder on D Apply OK
You can do this for as many of the folders as you wish, photos, downloads, music etc.