If you're looking for "proper" longhaul, TLV Tel Aviv might be the answer.

It's got a decent climate for that time of year.

You arrive in time to go walking on the beach at sunset and there's a nice Intercontinental on the beach there:



...once you've relaxed a few nights there, take a taxi to Jerusalem for some historical sightseeing such as the Wailing Wall and the Yad Vashem Holocaust Museum (though given the reason for your trip, that one might not be appropriate).



Sightseeing done, the highlight would be a few days at a Dead Sea Spa Resort to take the water...



...and get up pre-dawn to see the sunrise from Herod's lost city of Masada, which might provide a cathartic and memorable moment to remember your grandmother:



It's 62500 rtn in F, but your could outbound in F (Concorde Rm etc) and inbound in WT+ for 50k rtn on the nose, and both are day flights so you get to enjoy being in F and no need for a bed on the return.

You might struggle with availability this close to travel, though, in which case you really can't go wrong with NYC, except that decent accommodation can be pricey, and it's quite an energetic place to visit - maybe somewhere more restful might be better?

Muscat in paid WT+ upgraded with Avios to J and fits the bill nicely, as an alternative. And don't forget the pink sand beaches of Bermuda from Gatwick, though hotels and other expenses can be astronomical!



Otherwise, if you can cope with "just" CE, then Morocco (assuming no revolution) has some lovely resorts and sightseeing.