My condolences on your mother's passing.
You would not include her as a disregarded member of the partnership since the partnership was not created until after she passed and no longer owned the LLC. The partnership is a new entity with you and your sister.
Any business related income earned or expenses incurred before her death would be included on her final 1040. Everything after that would be included on the 1065.
The first return would be a short year from March to December 31, 2024.
You would leave the starting balances on the balance sheet blank and show the cash, land, building, etc as contributions.
