Difficult client advice please

I would like some advice please. Sorry this might be a long story.

My sister photographed a wedding on Saturday and sent the client some previews. The husband replied with positivity and the wife the following day responded saying that she didn't like any of the photos and would like the raw images so she can choose which ones of herself she likes to be edited. There was no mention of preferred shots, angles or sides of her face in talks with the client before. My sister agreed that she would send her low resolution pictures so she can choose the ones of herself that she likes the best. (For a fee of £100). At first she agreed to this, but wasn't happy when she realized she wouldn't be able to download the pictures. She is now demanding all the raw photos, so she can download them and get her brother to edit them. She keeps saying how she has the right to the photos that she's paid for, and has even threatened to go to court, as she will not let this go if they are not happy.

I was just wondering if anyone has any advice on how they would handle this client?