You could argue that Iris’s secret talent would be acting like a matchmaker (much to the dismay of Max) which was said to have been from her own mother. It’s not so much the fact that Twilight’s a princess that she was pushing the shipping, but it’s a nice bonus.
If you guys have seen Dragon Ball Z, the idea is similar to when Chi Chi was initially against the thought of her son Gohan with Videl… till she learned she was rich and when she asked her son when they were going to be married, Gohan does a rice spit take. (Only difference between that and Iris is she’s not concerned one bit about money)