Cal, you can make it a 2x7, of course. Realistically, you want a good low range, like a 26 or 28 tooth chainring would offer, paired with a large cog in the rear. Biggest cog you're going to find on a Suntour New Winner, not Winner (they really messed up the naming) is 34 teeth. 32 teeth is the most common. Building these freewheels and repairing them used to be a big part of my job at Via Bicycle here in Philly. I was the only guy in town who did it; Suntour freewheels are also how I cut my teeth as a professional bike mechanic after high school back in NM too. Are you sure it has a freewheel? If it still has the XCD6000 hub/s then that's a Suntour microdrive cassette. Don't even bother trying to find one. If you want to build Lyn a bike that she's going to enjoy riding, switch to Shimano shifters and rear derailleur. The front can stay Suntour since it's friction, but the rear needs to index properly unless she's comfortable with friction, and I doubt that's the case.
You may need a flow chart for your options.
If it is still a Suntour cassette system, you should get the rear wheel replaced. Accushift is only for nerds like me to make work on the stand, take on a ride once, get frustrated then eventually swap to 7 or 8 speed Shimano. When I build bikes that I want to keep in the period, I go with NOS hubs from that era which will allow me to place cogs that are properly spaced for a Shimano XT 7 speed thumbshifter. This means 5 options: Shimano 7 speed Uniglide cassette, Shimano 7 speed Hyperglide with Uniglide small cog, Shimano 8 speed cassette, Shimano 7 speed freewheel (preferably 600 or Dura Ace), and finally a Suntour 7 speed freewheel. When set up properly, all five of these options will shift perfectly with 7 or 8 speed Shimano shifters. That is, if the shifter is paired with a Shimano rear derailleur.
If you need to change the rear wheel and it is spaced at 130mm which you want to maintain, your options for cassette are Shimano XT (M730 and M732) and first generation LX (most hubs are black during this period).
Your 130mm options for freewheel are incredibly varied, but in Shimano they will be either lower end or older XT, as well as 600 and Dura Ace. Remember that up to about 1992, Shimano 600 was still spec'd on mountain bikes with high end freewheels. There is no difference between 600 and XT anyway.
The Suntour freewheel hubs you can find are all over the quality spectrum, but there are many NOS sets of XC Pro (WTB greaseguard) and XC Comp out there for not much money. Incredibly beautiful hubs, the XC Pros are, and I wouldn't hesitate to ride on them. There is a caveat though, the cup and cone bearing hubs are easier to service even though the cachet of sealed cartridge bearing hubs may be enticing, I'd stay away from them for the long haul.
I can keep an eye out for parts for you. I'm always looking for stuff for my own fantasy builds anyway. First we need to know if it is currently set up with a hub spaced at 130 or 135mm, then if it is cassette or freewheel.
From the brake track wear, it looks like you should have the wheels rebuilt anyway.
One other thing I noticed is that it almost certainly has Pedersen Self Energizing cantilevers. These are for expert use, you already know, and should be replaced for regular riding.
Phil