The Jack (socket) on the Laptop is designed so that when a Jack Plug is inserted, the connection to the speakers is broken by physically opening a link to the speakers. As this is a mechanical process, the speakers cannot function until the headphones have been unplugged to restore the connection to them.

As the quality of many Laptop on-board speakers is often inferior to even the cheapest of headphones, one solution might be to get a two-way Jack connector and a set of small external speakers with their own volume control. She could then have both external speakers and headphones connected simultaneously, turning down the speaker volume if necessary when on a Skype call.