Legal Question in Business Law in Texas

Yes:

Texas Vernon's Texas Civil Statutes - Article 6132b-4.03. Information Regarding A Partnership

provides:

(b) Access to Books and Records. A partnership shall

provide access to its books and records to partners and their agents

and attorneys. The partnership shall provide former partners and

their agents and attorneys access to books and records pertaining

to the period during which the former partners were partners or for

any other proper purpose with respect to another period. The right

of access includes the opportunity to inspect and copy books and

records during ordinary business hours. A partnership may impose a

reasonable charge, covering the costs of labor and material, for

copies of documents furnished.

If your sister won't let you look at the books, have a lawyer write her and demand access.