Not sure what you're trying to achieve here m8. Are you wanting to add the new HDDs in while retaining the existing one? If so, then yes, that should be fine, although removing the windows install from the new HDDs would be a good idea (I'd use ubuntu and gparted for this as it doesn't use the windows folders at all and you can delete them easily)
If on the other hand, you want to replace the HDD in your wifes machine then, no (short of some serious technical jiggery-pokery - which doesn't always work in any case). The best solution is to get all the data onto one of the two disks, then format the other and install windows again. If it's an upgrade version of 7 that you've bought you'll probably need to install an old version of windows first.
Jabo