If it will fit in her oven...

Make sure her oven is preheated properly, 180 with no crackling (do it after, last). You will need to cook it for 40 mins per kg at least.
Allow slightly longer for bone, but make sure you elevate it in the pan on a rack or some halved carrots or onion ends.
Make sure it is not cold when you cook it either - you *can't* cook it straight from the fridge, it needs to come to temp first on the bench.

I would cook it 5 hours 45 mins, plus 30 mins covered with foil to finish. You will need to rest it a while too, a good half hour under foil and a couple of teatowels.

You will need to add time every time the oven is open, so if you have another place you could cook it at or a BBQ, I would suggest using them.

Good luck!! LOL Nice work, Dad!

ETA: When/if you take the crackling off, make sure you leave as much fat on the pork as you possibly can, not on the crackling.