Someone who uses a dating app while on a date is showing a strong lack of respect for the person they are meeting, is incredibly self-centered or has become so accustomed to using the dating app on a daily basis that they are unable to shake the addiction.
No matter how much you were enjoying the date before she started using the dating app, her behavior is still inexcusable.
You feel like you have gotten to know the person fairly well in that time and wonder if you will feel as good about them in real life as you have so far on the online dating site.