I'm not too helpful but I'm enjoying stalking Diana's plot line because its :chefs kiss:

I have a cousin - Anthea [Emrys's "sister" ] who is currently inactive and I'm in the process of pondering logistics of reactivating thanks to Kaytes Hecate plot.

And as Lynn says their mother died in 1880 under mysterious circumstances which caused both grief and anger because she was only in her forth year so that could be fun to play with- and possibly bring up some clearly supressed emotions on Anthea's part: aka she lost a family/auntlike entity (working off age gaps) mysteriously and then the following year her own mother also disappeared under mysterious circumstances. She may even be convinced that it was all connected and nobody looked into it thoroughly.

She will be quite disheartened to learn that it wasn't.

And in the land of coincidences - Diana's husbands' infidelity and her disappearance during her school years may have contributed to Anthea's decision to avoid men and marriage as a cautionary tale (also doesn't help she doesn't have much evidence in her life of a happy marriage).

So impact on Anthea about Diana's re-emergence: I suppose its up to you what exactly their relationship was like as Anthea would've been in her third-forth year at school. She doesn't particularly care what society or other people think so she's kinda like meh about the whole thing.

... my two other characters are minors and not particularly helpful? One of them is an animal obsessed 9 year old (Caroline Weasley) who would try and adopt a cat and keep it secret from everyone (She has tried to have a family of Puffskeins live under her bed) if you want to use that for the fate of one of the children? Greta is at Hogwarts and I'm pondering actually getting her a cat. Or something to look after.