new life for an old snake plant

Can anyone recommend a type of soil to use? It looks limp

Well, I'm no expert with snake plants, but I think they do fine in a very standard potting mix. Any idea why it might be limp? Any change in its environment recently? When you pull it out of the pot, try assessing whether it's root bound or if the roots have rotted or are too small for the pot. If rootbound, going up a pot size should be enough. If the roots are rotted, you might want to trim the dead sections and pot down a size until it recovers...

well it was root bound and my dd repotted it in a larger pot and standard potting soil. It hasn't recovered. It is
limp and some of its leaves are getting brown spots.
So I moved it to a slightly more public well lit area to get
more attention and it is not improving.

She thinks she has a black thumb

ok, my book says that underwatering it will not hurt it at all, but it is prone to overwatering - lethal results. So defintely let it dry quite a bit, especially after potting it up. Apparently it's another of those plants that survive in low light, but really prefer warm and sunny.
Disclaimer: I don't use this particular book at all so it's advice might be totally off....l.

Try cutting one or two of the older leaves off of each plant. When it was repotted, roots might have been damaged and now the plant doesn't have enough of a root system to support all the leaves. That's my guess, anyway, and it won't hurt to do that.

What I read says that snake plants come from a climate with wet summers and dry winters. I have three clumps of snake plant. One is in the house in a darkish room but it does get bright morning sun through the gaps in the Venician blinds. We watch t.v. in that room, so it gets some artificial light when there is a Lakers, Clippers, Dodgers, or Angels game on t.v. :-) That plant gets watered every other week, approximately. Another clump is on the back porch. It gets bright light all day and some full sun in the evening. That clump gets watered once a week in the summer and once a month in the winter. The third clump is planted in the ground. It gets pretty much full sun in the winter and dappled shade in the summer. I water it once a week in the summer if I remember and in the winter, it fends for itself. (We have dry summers and when we get rain, it is in the winter.) The clump on the porch is the most vigorous. I thinned it two or three years ago and it needs it again.

Here is a mundane picture of the plant in the house.

This is the plant on the back porch. You can see how tall it gets and maybe can notice that it is starting to push the pot out of round. My plants are planted in regular ol' potting soil, nothing special.

thanks for your advice - I will tell her to back off the watering.