alam2 - Yaktrax have elastic which goes round the welt of the shoe and over the heel and toe, with the springs crossing the sole underneath. You put on your shoes, then fit the toe of each shoe into the elastic and pull the heel bit up over the shoe heel. You do need to sit down for this, unless you can hang onto something and work with one hand, and you need to be able to reach your heel - you'll know whether your 87-yr old MIL can do this. I put them onto a pair of ankle boots and left them on there even when I took the boots off - saved putting them on each time.
If she is using them only near the house, she can sit down in her own kitchen to take them off, supermarkets are a bit trickier. They say not to wear them on hard shiny surfaces as you can skid about, but I found that supermarket floors were no problem if I walked steadily and did not do a sudden turn, so I did not always take them off inside.
It is worth tying them onto the boots somehow with bootlaces if you can, then if one comes off in deep snow (as DHs did) it will still be dangling from the boot.
I believe the Yaktrax spring ones are better than the ones with little studs, but I have only tried Yaktrax so can't swear to that.
They are only about £10, so it won't break the bank if they prove unsuitable.
