They dont want her to go out because they dont want to tempt fate.
They are obviously ecstatic that their daughter has hit the jackpot in falling for a foriegner and now they are keeping her in because they know full well that there will be lots of Filipinos that will find her more attractive because of ££££`s she will have in her foreign bank account in future years.
There are many English and American guys that marry Filipinas with no idea of the "other guy" back in Pinoy land..
Im sure that your girl has no intention of looking elsewhere but trust her parents instincts,as in this case they know exactly what they are doing..