OK, just wanted to comment on the fence.
Do you own or rent? If you rent this might be harder as it is the owner who holds the rights (I think)
The land must belong to one of you, OR it may be a shared path as sometimes happens.
If it is yours, or shared, then it cannot be completely contained in her garden, ie behind her fence.
If the fence was put up by her, but is on your land, you are entitled to remove it, but you must not damage it, and must return it to her.
So, if the land is yours, and it has her fence, (and her spikes) on your land, you can remove it and return it. To start with, if it is on your land, you can remove the spikes, as they are on your land)
In reality, it is always better to do things nicely rather than start a dispute, so I would go round with a map, and show her that the land is yours. The politely suggest that you remove her fence and put up a fence of your own along the boundary line. (this can be a simple wire fence) If she needs/wants a better fence, she can put it along her side of the boundary, but you do not have to put anything there if you don't want to.
If she is unco-operative, then put it in writing, with a copy of the map, and say that on xx date you will remove the fence, return it to her and put up your own fence on the boundary line.
Don't get drawn into any discussion about how much money she has spent on that strip of land (not your problem, she is welcome to lift and re-use the gravel and grass elsewhere in her garden) or discussions over how useful that bit of land is for her and how useless for you (not the point, it is yours, you can use it as you like)
But if the land is yours, you should get it back. At the very least it is a legal annoyance that needs sorting if you ever sell.