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I may be able to help. Could you give me an example of this curse?

If you havn't already I think you need to talk to your grandma about this, tell (as nicely as you can) how she is mistreating your mom. If that doesn't work I found a few spells that may help. The first one I would only use it if all eles fails, the second one I think is somthing that you are more after.
To Change Someone's Behavior
If there is a person who is your friend/enemy/whatever and they are treating you badly you can change their personality so it suits you i.e. they act how you want them to do.
There are two different methods to this spell depending on whether the person is with you or not.
If they are with you, concentrate on them and whilst staring at them say the following...
"Twist their bones and bend their back, Hypnotic and mystic and magick and mystery."
Now carry on like that but change the first line each time you do it saying what you want them to be like and after every line say "hypnotic and mystic and magick and mystery".
When you have finished (it can be as long or short as you want) you need to raise your left hand
to their left hand side and say "just" then raise your right hand to their right hand side and say "like"
then you bring your hands together and draw them down the person's body and when they meet say "this."
By the way you don't touch them you just look at them and do it!

If they are not with you need to get a spoon (the bigger the better) and then you need to visualize them floating above you. As you are saying the exact same spell as above hold the spoon by the end and hold it vertically.
As you are saying the spell visualize its power building in the cupped bit of the spoon.
When you have finished the main part of the spell, you pull the spoon backwards saying "just"
then throw it forward whilst saying "like" and as you visualize the power of the spell hitting the person say "this."
Spell to make someone realize they've done wrong
To have someone see his errors.
This is a three times three spell to use on people who were corrupt in their ways.
It has no negative consequence unless you think ill of the person while casting the spell.

"Wind in the north, run through the trees
Three times three, let them see, let them see
Sands of the east, rich soils beneath
Three times three, set them free, set them free
Fires in the south, awaken from sleep
Three times three, let them see, let them see
Water of the west, flow to the seas
Three times three, set them free, set them free

It works best if you have something representing that person, like a strand of their hair or a fingernail. The spell may not work instantaneously, you may have to repeat it for the person to see error in their ways.

Mind you I didn't write either of these but I used the second one and it worked. I wish you luck, but please forgive your grandmother, she is might be slightly senile and not know what she is saying.

I found one a while ago with the candle in the cauldron of water. I will go look for it.