I agree. And isn't his mom living with him or vice versa? PF's Mom might not like KB moving in and if PF's Mom is going to be living with them after the wedding, they will need a 3 BR house. Maybe they were saving for that, ergo no set date. Also, no big wedding after baby was born because of religion.
The only reason I can see why KB would leave would be breaking up with PF. If she did, she walked out of the house with nothing but her purse and phone.
According to KB's mom, KB said she might go out for dinner per their phone convo. So maybe someone picked her up for dinner. That's somewhere you would go with only your purse and phone, not in your own vehicle.