"it seems likely to me that the neighbor may be using, not only the portion which lies on the easement proper, but also part of the driveway...

Question

"it seems likely to me that the neighbor may be using, not only the portion which lies on the easement proper, but also part of the driveway that is on your own lot. The neighbor cannot do this without obtaining an easement from you, because you are the owner of the underlying land from the boundary on back"

Actually our property line ends at the end of the easement, so technically they are not going over our property just the easement, but the curbing that was on the edge of the easement where they cut space out to put their gate in has now eroded all of the asphalt in front of our gate and there has been no maintenance agreement or anything. It just doesn't seem like it's legal considering she could give herself an easement on her own property to her back house. Do we really have no legal standing to deny her access to the private road easement we have in our deed from when the property was originally subdivided?

Answer

As I told you when you first posted this question, unless the grant of easement was exclusive, the owner of the house in front of your property had every legal right to grant additional easements in the same location and you have no legal standing of any kind to object. What you do have a right to object to and demand correction or sue for is the damage to your curb and asphalt. The one other piece of silver lining to this is that all legal users of an easement must share in the cost of repairs and maintenance, but the owners of the property on which the easement exists have NO obligation for maintenance or repair, so whenever the driveway needs resurfacing or other repair, the owners of the new house will have to share that expense with you, whereas before it would have been 100% yours.

Answer

I agree. You don't have an exclusive right to use the easement. The property owner, not the easement owner, can decide who else may drive over the easement. However, all users of a shared easement must contribute to its maintenance in proportion to their useage. Further, if a particular maintenance issue is attributable to the fault of user X, then user X is liable for the full cost of that particular repair.