Those shorts are made for La Femme 1. It looks like you are trying to conform them to La Femme 2. Their bodies are shaped differently which is why you are getting the pokethrough (they aren't slipping). ALWAYS be sure to confirm that you are adding clothing that was made for the figure you are dressing. Otherwise you will need to convert it. And converting involves rigging and weight mapping which is typically an advanced skill. But, here's how you convert LF1 clothing to LF2.

Afrodite included a prefit rig in the La Femme 2 Pro package. Her instructions.

(I would create a scene with no characters in it first).

1. Import the clothing's obj from the geometries folder into Poser

2. Load LF2 Pro's LF1 to LF2 Prefit Tool from the props library

3. Copy the LF2 shape morph from the tool to the clothing obj

4. Export that obj

Now you can import that obj in a new scene and take it through the fitting room or setup room :) Using the dev rigs as donor will be better than using LF2 herself, but both will work as a start. Remember to Copy Joints From after that, if you're in Poser13. 

(EDIT TO ADD: After you complete the conversion, save the converted clothing to your library so you don't have to do it again. Don't overwrite the LF1 version.)