sansevieria root system isn't improving

My mother inlaw gave me this plant along with several others she's had for years and she was neglecting. This one was actually her mother's and is close to 30 years old. It was huge a few years ago and due to her loss of interest in her plants fell into a rather quick decline.

The stalks which were brown and splitting when I received it have seemed to regain some life, however my main concern is the root system. I have had it for about 6 months now and I have it in cactus mix, as well as a clay pot. I only water when the soil feels dry, but the root system doesn't seem to be recovering, the stalks are growing, but they fall over, uprootring themselves frequently. I know they prefer only a little water, hate wet feet and don't require much fertilizer and I know it's way better than before I got it, but...

What more can I do to get this old plant back into a thouroughly healthy condition?

the plant may be wetter than you think. Maybe somehow, water is not draining well enough. The only way to find out for sure is to get the plant out of the pot and examine the roots. The plant doesn't look in dire straights so there's a pretty good chance you can correct. But you're gonna have to get dirty to find out. Also do keep in mind that tall leaves will flop. good luck.

I use a dowel rod to test the soil, straight to the bottom of the pot, if it comes up damp or dirty I don't water, I also have huge drainage holes in that clay pot, and clay is supposed to help whisk away excess water, or so I've been told. I recently repotted it due to my two year old emptying most of its dirt onto my floor, however none of the roots were damaged in her antics and the roots were solid and dry, normal looking, nothing mushy, nothing dark colored and no foul smells.

I'm not losing any roots, I'm just not getting any new ones back from what was lost before I became its owner

If possible, I'd move it to a brighter spot.

It gets direct sunlight for most of the day and partial sunlight the rest of the day. Yesterday was cloudy, so the picture is deceiving lighting wise. Thank you guys for the help, I appreciate it. I researched as much as I possibly could about the plant before attempting to revive the thing.. Maybe it's just the age of the plant that's slowing its recovery. I'm not sure how long they normally live, but this one is definitely old

They live indefinitely, though individual leaves & rosettes will come & go. The clump my gramma gave me about 20 yrs ago had been her plant for about 50-60 yrs. Older rosettes do peter out and stop growing, and new pups form from the roots. You will almost surely see some new pups coming up soon.

Sounds like that window faces south, that's about as much light as possible from inside. In that unglazed pot and cactus soil, you really don't need to be so concerned about overwatering. That usually happens with a plastic pot & peaty potting soil with no air in it. As long as the mix is chunky/porous/airy, roots won't rot while moist. Yes, Sans rot more easily than a lot of plants from wrongly moist conditions, but they are not cacti. If thirsty, they need water. If roots aren't growing enough to hold these up after 6 months, I think it's just been too dry. Water thoroughly, then let dry reasonably (not like a desert,) then definitely water again.