The way your phrase this question, the answer is 'generally yes'. There are steps such as a power of attorney that can be accomplished that will achieve what you need and may NOT require both parents however. The domestic court's orders (if any) and the father's status may also impact what can and cannot be done, so it is important to look at those issues before taking any steps as well. "Guardianship" temporary or otherwise, is usually a bad option, (but not always!) so it is important to look at all options to get toward your goal rather than fixing on something specific too early on in the process.
Your sister should consult with a local attorney (my main office is in Howell and I'd be happy to set up a time to meet with her if that is convenient) to determine both how the family court orders (if any) impact what can be done, and she should be sure to bring all the paperwork concerning custody, parenting time and the like as well as whatever other documents she feels will be helpful with her to the appointment.
I agree with Attorney Zichi that is it generally advisable to avoid a probate court action for guardianship, if at all possible. You eliminate the court costs and attorney fees, as well as the need to give notice to the father.
A Power of Attorney delegating parental authority will accomplish what you want to do. The statute allows for this to be done, for a period of 6 months at a time. Additional delegations can be made, if more than six months are needed. The father does not need to consent to this, or be notified.
If the father has not had his rights otherwise terminated, yes. That said, I agree with my colleagues. Why go through the public process of the probate system when you can potentially take care of the matter in a private fashion.
Also, consider the danger of limited guardianships. There is a placement plan that must be entered into. If the parents fail to meet the terms, they could potentially lose their parental rights!!!!