It seems that a powerful tool like Lightroom (on top of a powerful Adobe suite) should allow a developer to import a client's catalog from Photoshop Elements on an external hard drive. Everything I've read in the support and forums indicate I need to have Photoshop Elements installed on my own machine, and that reading off a network drive is not possible.
As I understand things, yes, you have to have PSE installed on your computer to make use of the PSE catalog in Lightroom. I can't understand why Adobe would program things this way, but apparently they did.
A possible workaround is to have the PSE owner install the 30-day free trial of Lightroom on his/her computer, have that person upgrade the PSE catalog to a Lightroom catalog, and then send you the catalog file.
Yes, Lightroom can import a Photoshop Elements catalog, but there are restrictions.
Let me know if there are questions that this does not answer: