If you remove her name from the LLC, it automatically reverts to a Disregarded Entity and no elections need to be filed. For simplicity, it would be ideal to do that on December 31st.
If you remove her name from the LLC, no, the LLC does not need to get a new EIN. However, for most purposes (other than having employees) when a Single-Member LLC is a Disregarded Entity, it should use YOUR Social Security Number or EIN rather than the EIN of the LLC (see the instructions for Form W-9, Part 1).
