Gentile at the Seder

The main halachic concern about inviting a gentile for a yom tov meal, is that one may not
cook for him/her on yom tov, since we are allowed to cook for ourselves on yom tov, as
opposed to Shabbat. Thus, there is no prohibition of inviting a non-Jew for a Shabbat meal,
since we are not going to cook on Shabbat in any case.

If a gentile comes uninvited, there is no problem in serving him food that has already been
cooked, as long as nothing will be cooked especially for him on the yom tov. But, if we invite
him/her in advance, we may cook something especially for them, as we do for guests in
general to honor them.

If a Jew is intermarried, one may invite them even if we know their spouse/family is not Jewish, in order not to disrupt the joy of the festival.
Therefore it is permissible to invite the non-Jewish woman to the Seder this year when it, falls on Shabbat.