Yeh Hai Chahatein: Why is Preesha upset during mehndi ceremony?

In the serial Yeh Hai Chahatein, Preesha's mehndi ceremony is taking place. But why is she upset during her own pre-wedding rituals? Preesha is all set to marry Armaan but she is not feeling good about her own decision. Why is Preesha missing Krishna now? Are Preesha and Krishna related to each other? Will this marriage take place?