Current Setup (Please correct if otherwise):
AC on a Laptop - Wife has it during business hours. You have it afterwards.

Recommendation:
  • Get Desktop - Move Database to It. Make sure this is a good one. Windows 7 Pro 64 bit, 8GB RAM, i5/i7, etc. Setup Remote Access using LMI/RDP. Use concurrent sessions tweak to have concurrent users logged in meaning you can both we working remotely. Demo here: https://www.youtube.com/watch?v=l4bAlp52z1A
    Well-Priced Examples (There are better ones, but these are available fast):
    - Lenovo ThinkCentre 0958B2U Desktop (Free 2 Day Shipping Fast (Amazon Prime), Windows 7 Pro, i5-2320, 4GB RAM, 500GB HDD)
    - Acer Veriton DT.VC5AA.002 Desktop (Free 2 Day Shipping Fast (Amazon Prime), Windows 7 Pro, i7-2600, 4GB RAM, 500GB HDD)
    ==>+4GB RAM is $20
  • Keep the extra computer at home - Since you will be working remotely, the speed of your computer is irrelevant for the most part. Just get a good size screen. You could use that desktop you already have.

You will have to be extra careful since you will be working directly on the server. Your wife can either connect via LAN (wire) to access AC using her laptop or via WiFi to the main computer over RDP. As I said earlier, you will have to be careful with working directly on the server. 100 FT cables are $10. She could keep the wire where she usually likes to sit and get a cart for the laptop. Just get 2, one for each exam room.

When she is off-site, she can either use remote access or just keep a note in a plain text file and copy it to AC later (encrypt or something too). I wouldn't go through the hassle of setting up 4G and all that if she's seeing only one or two patients on the way home, sometimes.

When you are at home, you can use Remote Desktop and it'll be as if you're sitting in the office. Not a bad idea to get Skype on your computer as well as her laptop so you can communicate.

Once the practice gets going, you can get a proper setup.