For street walking for your mom, you'll want rubber tips on the poles. Most poles come with metal tips and you buy the rubber things separately to cover the metal. Overall weight is one important factor in shopping, as well as the comfort of the hand grips and straps. I've had Komperdell poles and REI brand (on my 3rd pair). Leki is known for good service. The expansion bolts become problematic after a couple of years - you have to oil them regularly to keep them working, but then if they fail in the locked position and you can't loosen the joints, you're screwed. If they fail in the open position, you can usually pull them out and lube them. Some companies use lever-activated joints rather than twist-activated joints. The lever-activated may be more reliable, but I haven't tried them.
Pole length should be set to hand height with elbows bent 90 degrees and forearms parallel to the ground. But hikers will adjust them longer or shorter depending on the slope and terrain (longer for downhills, shorter for uphills). If you get the adjustable poles you can always make them right (just be aware that ultralight poles may be too short for tall people).
Oil is good, grease is better.
2007 Peter Mooney w/S&S couplers/Terry Butterfly
1993 Bridgestone MB-3/Avocet O2 Air 40W
1980 Columbus Frame with 1970 Campy parts
1954 Raleigh 3-speed/Brooks B72