Well the problem here to me is:
1) That family member, does not have the guts to tell you herself. And instead relies on word of mouth and innuendo and gossip to convey her issue. Whether it is a lie or not, is to me, not the problem.
The problem is: that family member is alienating EVERYONE in the family and its tradition of round-robin-family-meals, but will not tell the lady of the house or her family, what the problem is. Not to your face.
And this has been going on for OVER 1 year already.
I would be over it by now.
It is an old drama... and it is toxic to everyone, but some want to play her game and allow her.. to do it.
NO ONE seems to call her out on it nor correct her.
So they are wrong too.
Meanwhile, it is alienating your family and it is all very discriminatory.
Whether or not she has a real truthful reason, or not.
The thing is, that step-family-in-law-member... has NOT discussed this WITH you. At all.
And no one can read her mind nor predict what her reasons are.
And she sounds like a drama-trouble-making-manipulative individual, whether or not she is telling the truth.
So if you give her the benefit of the doubt, you will be doing it without knowing for a fact, what the real truth is, or if it is even her allergies or not.
And it is your choice to do so.
And it is your choice... to get tangled up with a Toxic person like that, or not.
Meaning, if it is not this issue of hers... she will always create other problems. Her history of that, precedes her.
The woman is a CHRONIC drama queen.... and she will ALWAYS be that way... and she will ALWAYS hold everyone as her emotional hostage or victim.
And also the other family members do not have the guts, to correct her or to go against her wishes nor do they have the guts to stand UP to her. Meaning, everyone seems to be doing what she wants them to. Including her Husband probably.
And now they all, are alienating you.
I would not, ask her to be invited to her house.
Why? She is so toxic. I wouldn't want to be in her house at all.
She seems to be THE big Bully, in the entire family.
And they all listen to her.