Tu hija se está por casar con un buen hombre
[Caption 17, Provócame > Pilot > 7]
When Patricia says to Ignacio, Tu hija se está por casar con un buen hombre she is saying, "Your daughter is about to get married to a good man." Estar por hacer algo can be interpreted as "to be about to do something." Note that the reflexive pronoun se in Partricia's phrase belongs to casar, not estar; she could have just as well have said Tu hija está por casarse.
Está por llover.
"It's about to rain."
Está por llegar.
"He/She's about to arrive."
Estábamos por comer.
"We were about to eat."
Provócame is an Argentine program. In some Spanish speaking areas (not Argentina) estar por + infinitive can indicate an inclination to do something, or to be in the mood to do something. Likewise, in some (other) regions, estar para + infinitive is the more common way to indicate that an action will soon take place.