However, you could consider these options:
* Siân: This is a popular Welsh name that is sometimes used as a shortened version of "Jane". It's pronounced "See-on".
* Siâned: This is a longer form of "Siân" and is a more formal version.
* Jana: This is a Welsh name that is similar to "Janet". It's pronounced "Yah-na".
Ultimately, the best way to choose a Welsh name for Janet would be to consider her personality and what name resonates with you the most.