As her dowry, she brought the Lordships of Blamont, Châtelot, Belmont, and Cuisance into the marriage.

The Lords of Neufchâtel-en-Bourgogne placed Blamont under the protection of the Duke of Burgundy and thus detached it from Montbéliard.

They had five children: In 1283, her great-grandfather, Theodoric III, Count of Montbéliard (1205–1283) died.

He had outlived all his children and in his will, he left the County of Montbéliard to his great-granddaughter Guillemette.

Theobald III of Neufchâtel, who was a grandchild of Theodoric III and who wanted Montbéliard for himself, conspired with Reginald's brother Otto IV to have Montbéliard recognized as a fief of Burgundy.