Guardianship is the propety procedure and should be filed promptly with a request for immediate termporary guardianship so you have the legal authority to consent to medical care if needed in an emergency. The consent of the mother is very helpful, as will be the testimony of the child (who should definitely be spared the stress of sitting in the witness chair by involving a guardian ad litem or requesting in chambers interview by the judge) as it will be necessary to prove that the parents are unable to properly parent the child. Whether a guardian's ward can be covered on the guardian's insurance depends on the insurance company, but it is unlikely. To ease your journey through the legal system, the assistance of an experienced family law attorney is definitely needed.
Best wishes for a favorable result in the best interests of this child, and please remember to designate a best answer.
This answer is offered as a public service for general information only and may not be relied upon as legal advice.
You should speak to an experienced attorney in your area. In Oregon, to file for guardianship or custody, you need to prove that you have a parent-child relationship with your niece and that the relationship has existed for at least six months. If you do not meet this threshold, there may be other options.
To advise you an attorney will really need to talk to you at some length to get a better idea of the family issues. The biological parents have a constitutional right to parent their child over the any other party, whether the issue is guardianship or custody. So if you start to get involved in a formal process one or the other parent might object and absent proof that they are some how unfit to parent, you will lose. While her thoughts and feelings can be considered, a 13 year old child doesn't get to chose where she wants to live. So an attorney really needs to help you figure out if you have a situation where setting up guardianship or custody will be appropriate. Anyone can apply to be a guardian - there is no requirement that you have a parent child relationship for 6 months. There is however a statute in Oregon that gives someone with a 6 month relationship with the child the level of a psychological parent and that gives them the right to apply for custody. However there is still a case that came down from the United States Supreme Court that stated that the biological parents have the constitutional right over other people to get custody of their children and there needs to be a pretty strong showing of detriment to the child to over come that right.
Without knowing more of your situation, I just want to point out that there is a statutory form under ORS 109.056.that can give you the right to be a temporary guardian for a child. The form says that it is good for 6 months, but one method to extend it is have the parents pre-sign additional delegations for subsequent 6 month periods. It doesn't require formal court proceedings and the parents can revoke it, however I have had client's report that the form was enough to give the person in your position the ability to get them medical insurance, enrolled in school and to take them for medical treatment. Maybe this form would work for you in this situation as a temporary measure and be acceptable to both of the parents. This might at least be a way to address the immediate logistic problems while your niece and her parents work things out.
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