This area of law is complex. You need to speak to an attorney well-versed in easements and real estate. Eau Claire has plenty. Do a Google search or check the yellow pages. You seem to have a good claim, but this kind of thing can get tricky fast. Good luck!
From the sound of it, the driveway is on the other property, but the deeds to both properties gives your mother's an "easement" (think of it as a right of way) over that property to get to and from hers. If bothe deeds have this right of easement, then the "dominant" estate (property) owner can not prevent your mother from using the driveway. If they are, you would need to go to court to enforce the easement. You need to consult with a Real Estate attorney in your area as to how to proceed, as these types of matters are quite complicated and can have different rules from one jurisdiction to another.
Your question states your fear of blockage that may or may not be real.
Find a time to speak to the neighbor that is not rushed. If you can talk civilly and not reach an understanding, offer to go to a mediation service with the neighbor.
As the attorney answers also indicate there are Eau Claire attorneys that can pursue legal remedies.
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