Simply present yourselves as you are., serve the same meals and do the usual things. perhaps make a few concessions on food, chips with meals and plenty of bread and butter.
Let conversation arise from your everyday lives. How was her journey, hpw long did it take, comments about any roads she may have used, towns or countryside she may have gone through and so on.
She is your husband's child and you barely know her. Expect him to be the active partner in this visit. Ideas are to
find something to do together, perhaps visit a beauty spot, a garden. If she is obese, she may not want to walk very far, but even this time of year, some outside places are nice to visit and will have a cafe serving tea and cakes.
Just relax and be your self.