There are several pencil kits that are top notch in my opinion. I keep 2 pencils on my office desk, a BHW El Grande which uses a Schmidt mechanism and a PSI Executive. The El Grande is a larger pencil, about 1/2" in diameter, and it is quite light, weighing no more than the Executive which is about 3/8" in diameter. You can also get 2 very classic pencil kits from BHW; one is styled after the 1940's Parker Twist pencil, called the All American Flat Top Double Twist and the other is styled after the German Mont Blanc Meisterstuck Classique twist pencil call the European Round Top Double Twist pencil. All 4 of these are lovely pencil kits and any of them would make a very nice birthday present for your mother-in-law. Just a note, the El Grande is convertible to a Parker-style ball point just by removing the pencil mechanism and inserting the ball point refill.
I have also converted a number of pens to pencil. I have purchased the pencil mechanisms from both Bear Woods and I think Exotic blanks. Some pens take the conversion with no alterations some others need a little coaxing.
Greetings from Nebraska - the answers already provided are sound.
I like the DuraClick EDC from PSI which is a 0.7mm lead (wish it was available with 0.9mm though). It reminds me of the Pentel GraphGear 500 series that I use in my shop.
I have also used the aforementioned 0.7mm Schmidt Converters with good success to turn a Cigar Pen into a Cigar Pencil.