Good present
. As Sally says, see if you can post us some pics of the wheel on here. If your MiL bought it new in the '70s then it's likely to be an Ashford Traddy, single treadle, Scotch tension. If so, then just about everyone knows how to use one so you will get plenty of advice.
For how to renovate it, Dans may also be able to help as she has restored the one of similar vintage that my aunt gave her. Sally has done several too of course.
You may need to clean the wood before you start Danish oiling it (or you could lacquer it, but Danish oil is much more satisfying and makes the wheel feel loved
) . I'm not sure how best to clean it as it depends on what is making it dirty. If it's just the years stored in the attic then something simple will do, but if your MiL used unwashed fleece then there could be years of dirty lanolin to clean off first.
You might also want to fit a new synthetic driveband (Scottish Fibres and Winghamwoolwork sell them) and a new piece of fishing line for the tensioner. The bit which connects the foot plate to the crank bit at the back was of leather in the 70s but spares are still obtainable and should be kept supple with oil.
If the wheel has got a bit damp in the attic then you might also want to replace the yarn hooks on the flyer if they are rusty and pay attention to the inside of the orifice as if that's rusty then it will catch the fibres.
As well as treating the wood, you should oil your wheel (gun oil, again from Winghamwoolworks, or any light machine oil) a few times before you start, then every few days after that. Once we see pics of the wheel we can suggest where you should oil, but basically anything that moves.