Install the app, but see something unexpected.

You install the app and open it discovering instantly that all of the data is different to hers. After longer than you would like to admit you realize that the app is showing you your own stats, not hers. You see a button that lets you pick anyone on your friends list to change, currently just you and Carrie, you switch to hers and test a few things, making her a little taller and shorter seeing that the changes are quick but not instant.

You set her height back to normal then fiddle with the mental settings changing her loyalty to you from 60% to 100%

While you are at it you change your stats around a little making yourself taller, smarter, stronger, and giving yourself a slightly bigger dick (it was already pretty big)