Merwyna can be another form. https://oswinkinsey.wordpress.com/ [See document titled "English Compound Names". 'Merwyna' is at page 120])Merwenn is a variant listed in the Submitted Names Database along with Merewen, Merewenna, Merewin, Merewina, Meriwenna, Merwenna and Merwinna.
Merwenn is a variant listed in the Submitted Names Database along with Merewen, Merewenna, Merewin, Merewina, Meriwenna, Merwenna and Merwinna.