Legal Question in Business Law in Illinois

I assume you mean to ask if your wife is entitled to anything, not your sister.

Usually in those cases the partners in the busines have a agreement about how the death of one will afffect the business. In many cases, there can be a finanical interest of the deceased partner that will be allocated to its heirs. Or the interest just reverts back to the partnership and is distributed across the remaining partners.

So the question really cannot be answered conclusively here. She should seek the advice of a wills/probate/estates lawyer near her and inquire about how to approach that.