Check out Bontrager H2 tires. They work great as a commuter tire for mixed surfaces and aren't very expensive.
+1 on not sinking a bunch of money into this bike to start with. Make sure your wife likes the bike and riding then make changes as needed. Clean, lube and adjust everything. Repack all the bearings. If the chain only has light surface rust, I'd lube it up and ride it for a while. I wouldn't replace the fork right away unless it it shot or your wife really hates it. Fog a bit of WD40 or Liquid Wrench Penetrating Lubricant (blue can, different from the Liquid Wrench in the yellow can which is used to break parts free) into the shifters and work them through all the gears a few times. Cables can be lubricated by loosening them enough that the housings can be freed from the stops, wipe the cable with lube and slide the housing back and forth along it a few times adding a drop of lube to the cable at each end of the housing until it slides smoothly and freely. Place the housings back in the stops and readjust the cable. New brake pads and cleaning the braking surface is a good idea, old pads get stiff over time.
My wife rides an old 820 as a commuter, here are some of the changes I made for her:
- Profile design stem that is shorter and has a more upward angle than the original stem
- Handlebar with a bit of rise and sweep
- Ergon GR2 bar end grips
- Bontrager H2 tires in 1.5" width
- She insisted on a "comfort" seat but I'm trying to talk her back into something more like an endurance/touring saddle
You may or may not need/want to make some of these changes, this is just a list of what worked for my wife.