Hi Patricia, my apologies for the delayed response.
A 2 person LLC is generally considered a partnership and should file Form 1065 to calculate the tax liability for a business. Any taxes due will pass thru to you and your sister’s personal tax returns. (The instructions from Form 1065 will tell you how to report this on your personal tax return).
Here is the link to our LLC tax guide where you can learn more about the required tax forms and reporting requirements for LLCs: https://fitsmallbusiness.com/llc-taxes-tax-returns/