Without having to contact Dell support, and suffer whatever delays they may incur, your options are fairly limited:
To use the original license that came with her laptop, or another license that came pre-loaded on another system:
You will either need the Product Key which will be provided on a sticker attached to the system's case, or a tool like ProduKey which can recover the key from the HDD if it is still usable and has not been wiped.
You will also need an OEM install disc (These used to automatically ship with a new system. These days, you usually need to request them and pay a small fee.) for the OS - a Retail or Volume License installation image will not work.
Technically, using an OEM license on a system other than the one that was shipped with it is against Microsoft licensing terms. Using an OEM license on multiple systems at the same time is definitely against the license terms, and may cause problems with activation when two or more systems are recognized to still be active with the same Product Key.
To use a Retail license which was previously installed on her laptop, or another one that was previously used on another system:
You will need a Product Key, either from the retail package in which the installation disc came or obtained via a recovery tool like ProduKey.
You will also need a Retail installation disc (one that came in a package bought separately from the computer) - an OEM or Volume License installation image will not work.
Using a Retail license on multiple systems at the same time is against the Microsoft's license terms, and may cause problems with activation when two or more systems are recognized to still be active with the same Product Key.