I get so aggravated when I tell mom something for her own good and she doesn't listen. But let my absent sister or brother tell her the same thing I just did, she'll listen and do it. As her only caregiver, I do everything for her...always put her needs before mine. Is it I care too much?
She knows you aren't leaving and can speak her mind knowing you aren't going anywhere.
If you can't ignore it and it gets under your skin, nothing wrong with confronting her and saying "Mom, it really hurts me when you listen to Sister Carol, but you won't listen to me when I give you dip same advice? -- why do you do that mom?". Then repeat same mantra every time she does it.
Tell her that maybe she should love in with Carol since Carol seems to know what is best.
That may curtail it, or at least make you feel better.