Hmmm- Thought this might help but alot depends on the complexity of the photo and amount of similarity between colors in the object you want and those in the background. You can use a variety of sleelction tools in the selection process. Would look at what you think would be easiest to get rid of--sound like the background. Use the Lasso tool (point to point mode) to just do a quick outline to elliminate most of the background. Then switch to magic wand- you can adjust the tolerance to fine tune the selection and also may want to check the contiguous option---but if she has brown hair against a brown carpet- this may not work. Sometimes the magic wand leaves little bits unselected that are kind of tedious to go and click on each spot. This is when you would choose the selection brush (make sure it is set to add to selection and make sure your magic wand slection is still active) and use it to add in the unselected by brushing over them. As long as you keep your slection active - you could use all the different selection tools to make your selction.
But to escape briefly from the frustration---since you can already do the extraction process in iphoto- do it in there- save the file and then bring it into PSE? I don't use a Mac but I think primarily the only differences in PSE for Mac or windows is the keyboard shortcuts- everything esle should work the same. If iphoto won't save in a PNG format you could easily erase the wihte background in PSE (feather the slection by 1 or 2 pixels) that will be present when saved as a JPG. PSE is really a pretty powerful program for the price- hope you won't give up on it too soon. Could you post the photo in your gallery? That might help if we can see exactly what you are trying to do.

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