Im so sorry that you’re going through this whilst you are still in mourning. I hope advice on here will be helpful to you.
I’m a big lover and wearer of pearls.
Ive got lots of strings in different lengths with beautiful clasps etc.
I’ve recently had a double string with a diamond clasp restrung and made into an opera length necklace so you could say I have experience!
The silk will, with wear, soften and the length will definitely stretch a tiny bit. This will alleviate the kinks but only if you wear them regularly. (I can see they have been knotted individually.)
It might be that your Nan wore them a lot and you hadn’t realised quite how much they’d loosened and stretched? However, the box is quite telling about the original length. I’d wager some pearls have gone missing which is why I count and photograph my strings prior to restringing but hindsight is a wonderful thing.
Yours have been strung far too tight so take it back and ask for a refund so you can go elsewhere, or, tell them to use a different stringer next time.
Go into the shop with confidence and be absolutely certain about what you want the outcome to be. Go early in the day if you can, when minds are fresh. You could do a belt and braces and ring in advance to make sure the decision maker is at work.
Don’t be brow beaten. Offer them a choice, refund or re-do. Any decent jeweller with integrity will sort this out. IF it’s a jewellery chain, Google the head office and write to the CEO if you are not satisfied. Send pics. I’ve done that in the past and got something sorted out. Leave no stone unturned.
Good luck OP.