The crying over Christmas was pathetic.
That was a great opportunity to have your traditional Christmas on the 24th and a UK traditional Christmas on the 25th. She could have cooked a turkey crown (frozen, pre prepared, some Brussel sprouts & spuds, shop bought gravy, stuffing + frozen spuds. Boom. Christmas dinner; You or DH could easily do that.
She could and wrapped up £15 of big-looking presents and voila, Christmas 2.0. Freeze leftovers from the 25 th. Eat X2 Christmas leftovers on the 26th.
And here's a plan for a bank holiday Monday.
You drive 4 hours Friday morning. Get to Stratford upon Avon or whatever. Have a day out with your family. Stay overnight in whatever nearby Holiday inn. Then drive 4 hours the next day. She drives 2 hours towards you. You spend Saturday together. She drives 2 hours back in the evening, or if that is too taxing, she stays overnight there. You can all stay overnight there. Sunday you drive back 4/6 hours. Stay overnight somewhere. Monday morning, drive back 4 hours.
Grandmother seen. No annual leave used.
OR
Even if there aren't planes, I'm pretty sure there are fast trains for a good whack of the way. Pick her up an hour away. Have her keep a couple of outfits at your house, so that all she needs to bring is a handbag. E.g. if a pair of her trousers, shoes, pants & bra + cardigan live in a bag at your house she won't have to navigate a train with a suitcase. Just pack a couple of blouses.
Also if you say you're a passenger who needs special assistance they will usually get someone to take you to a connection.
If she doesn't drive and refuses to use public transport, then she's refusing to see her grandkids.