I have a Nook Tablet, and if it is not in the Nook app store, then you will not be able to get it. There is a very complicated way to get around this, but I have yet to figure it out. If your friend really wants to try, she can look on Google I suppose, but it sounds very difficult.
Also, the Nook Tablet does have an Andriod OS, but it is not a Google product and does not have access to the Andriod store like on Android cell phones.