If it's taking a really long time, often the problem is that the clothing intersects something already. That can lead to really long sim times and ugly results.

Make sure you're starting from a zero pose. The skirt should not be touching anything at the start of the sim, including furniture, etc. Clothify just the hip, not the entire garment (since this is a hybrid item). If she's sitting, you probably want to include the chair in the things the skirt collides with.