I'm not sure I've met your nanna..... :-)

A couple of different approaches

1. The Traditional Way

Lift the meat out of the roasting pan to rest and place the pan on the stove top over a low heat.
Add a tablespoon or so of flour to roasting pan and use a spoon or whisk to use the flour to mop up the fat and other meat juices that are in the pan.
Once all the flour is incorporated you should have a paste, or lumps of paste floating about in the meat juices depending on how much liquid was in the pan - try to break up the lumps with a whisk.
There should also be crusty bits of stuff cooked onto the pan...that stuff tastes great so we need to get it off and into the gravy - add a glass of wine (white for chicken, red for lamb or beef) and turn up the heat so that it starts to boil and bubble away, whilst it is doing that scrape all the stuck on bits off the bottom of the pan into the bubbling liquid.
Use a whisk to break up any lumps of flour, or lumps of sticky stuff....your nanna had strong wrists!
When the wine is nearly gone, add some stock to the pan and whisk it all together to make your gravy - taste it and see if it needs a little salt and pepper, then pour it through a sieve into whatever you are using to serve the gravy.

2. The Easy Way

Put the roasting pan on the stove over a low heat as before
Either use a pre-made roux (see the posts about cheese sauces) or just put a tablespoon of cornflour in the mug with some *cold* water and stir it together - if the water is warm then the flour will start to cook and go lumpy...if it is cold then it won't.
Add the glass of wine to the pan as before (you could go straight to the stock, but this gives it another level of flavour)
Scrape all the tasty bits off the bottom of the pan and boil the wine as before, then add the stock and throw in the mixture from the mug. Keep stirring as the stock comes to the boil and the gravy should thicken up nicely as the cornflour solution goes hunting for fat molecules to stick to.

Tali - a slow cooker is just a self-heating electric pot that doesn't need to be watched as carefully as one sitting on the hob. You can't do the frying parts of these recipes in them as they can't get that hot, but for the sections that need long slow cooking then they are great - just throw everything in, close the lid and get on with the rest of your day.