Can my sister keep me from my mom?

Lisao718,
Your profile says you are caring for your mom at home. Your post indicates sister is living with mom in moms home.
Was there a recent change in homes or caregivers?
Who has POA for mom? Does anyone?
Has your sister asked you not to visit your mom?
Is your mom incompetent to make her own decisions? Has she been diagnosed? What care does your mom require?
Give us more information about your situation for better answers.

lisao718, if your sister is your Mom's live-in caregiver, she probably doesn't call you because she doesn't have time and/or is so exhausted she just wants to crash and burn from the exhaustion.

Does your sister have any help with her caregiving? What are your Mom's health issues? Is she mobile? Does she have memory issues? Did your sister have to leave behind a family or a job to take care of Mom? That in itself can build up a lot of resentment.