The answer can be either simple or complicated.
Simply? A curse cannot affect anyone who does not let it. In fact, a lot of people get a bit psyched out over some 'bad luck' so to speak, and believe they're cursed.
But if your cousin wants something to do, in order to concrete the belief that a curse is ended for her, there are options.
Any of these, if done, must be done with clear and focused intent.
A cleansing ritual to rid the negative energy is a good place to start. A hot salt bath, visualizing the negativity being drawn into the water and running down the drain at the end is a common one. Any extra herbs (sage, for example), candles (white for purity and clean energy, black to absorb negative energy), incense (sanalwood for cleansing, or any, perhaps believing in the symbolism of the encompassing smoke and aroma), symbols in the bath, etc., will be a help.
A banishing ritual is also an option. There are many options where this is concerned, from the Lesser Banishing Ritual of the Pentagram, to visualizations, can be used to send the negativity away.
If she knows who sent the curse, and wants to send it back, there are Return-to-Sender spells out there.
Any of the above will do the trick, so to speak.
Finally, when your cousin believes the curse is ended, comes a ward and/or protection.
These mostly are in the realm of visualizations, directing intent.
One of them is to meditate. Clear one's mind, and focus on the visualization of a pure white (or whatever color chosen which best represents protection -- intent is more important than the specific color) light starting in the center of one's being, and growing to fill the body completely. This fills the body with the protective energy within, and it must also be without. One should direct the protective shield to begin on the ground beneath, growing into a disc. Eventually the edges rise from the ground, and completely surround the person, completely -- all around, above, and below. Negativity can leave. Positivity can enter and leaver. But no negative energy can penetrate from the outside. Throughout the day, one should take a moment to visualize the protective surrounding, reaffirming the belief it is there and its protection.
There are also means to make a protective charm, if it is desired.