Who is Sondrine from Something Blue and what is their importance?

Sondrine is Ethan's French girlfriend. When Sondrine meets Darcy at the Muffin Man, she is cordial enough. However, as her relationship with Ethan becomes more involved, Sondrine is concerned about Ethan and Darcy's living situation. When Sondrine and Ethan go on their second double date with Darcy and Geoffrey for Valentine's Day, Sondrine is visibly annoyed about Ethan setting up a baby nursery in his apartment. She is thrilled to hear from Geoffrey that he and Darcy are moving in together. Sondrine's joy is short-lived as Darcy has a pregnancy scare which leads to Ethan taking care of her while on bed rest for the remainder of her pregnancy.