My out of state sibling thinks it’s insensitive of me to tell her I’m sometimes overwhelmed. Any advice?

Ditto to what Eyerishlass and cwillie posted. Unfortunately, you can't pick your family. Even though you haven't provided details of who you're caring for and other situational info, please stop to consider that "sometimes feel overwhelmed" will probably eventually turn into "completely overwhelmed" if you are caring for an elderly person who is infirmed or has dementia -- they require more care, not the same or less, as time goes on. You should really start thinking about how to deal with this reality so you don't become burnt out (or broke or sick in some cases -- just read some of the other posts by on this forum). Blessings!

We all need someone to spew to when caregiving becomes too much but your sister clearly isn't it. This forum is a great place full of people who have been there, done that, it truly kept me sane!

Don't share your feelings with your sister anymore. She obviously isn't compassionate to your care giving role and while I understand your need to reach out for support from a sibling in this situation your sister isn't likely to be receptive to anything you may share about being a caregiver. Seek out other support among other family members, friends, and community.