How can I tell if Mom, who has COPD, is okay when I'm caring from a distance?

Eight months ago my mother was told she had six months to live. She has COPD. I live in Florida and she lives in Texas. I have offered to move there to help her (I am her only child) but she has these three people (two of which use to be her gardeners) that she says are taking "wonderful" care of her. It concerns me terribly, but she says she doesn't want me to come there. She is very hurtful and manipulative. Is this normal? I feel like I should be there taking care of my mom, but it appears my hands are tied.