Ideally, you would share your concerns with this person, perhaps suggesting that her behaviors have concerned you, and that you are worried about her health. There is a possibility, too, of course, that her behavior may be related to some physical condition or medication reaction, and she may be receptive to seeking health care. Sometimes it's easier to seek help for a physical problem.
If this is a friend, you can't do much else except be supportive to her and her family. If this is a family member, you can suggest (insist) that she see her health care provider, for whatever reason. (Talk to the provider in advance).
In my experience, unless the behaviors are really dangerous, you can't force treatment. It is very hard to make someone voluntarily cooperate with treatment they don't want.
If you think the person is truly dangerous or self destructive, in my state, there is a procedure for involuntary commitment, which would involve a visit to the county courthouse. (You could probably get this info from the state police). I have cared for many patients who were involuntarily committed. Usually the behaviors were outstandingly abnormal. You may fear the person will resent you committing them, but it's better than them hurting themselves or someone else, and once they receive treatment, they may understand where you were coming from.
Good luck. I feel for you.