It's possible to change the App Store country while using the same Apple ID.
Go to App Store - Featured or Settings - iTunes & App Stores. There, tap your Apple ID. Then select "View Apple ID". You'll have to enter your password, then you'll see "Country/Region" as third option, with your Apple ID as first one. Tap this, then you are able to choose a country. You'll need a payment method and an address for this country.
If you intend to keep this country in your App Store and not change back to the USA, this is what you can do.
If you want to change between App store countries, set up a second Apple ID with a Gmail address, a payment method and an address in the UK, then you can easily switch between both countries by signing out of the one Apple ID and signing in to the other one.
To set up a new Apple ID, you'll have to tap your current Apple ID and sign out. When you tap again, select "Create Apple ID" and use the Gmail email address, address from the UK and the payment method you prefer. "None" is also an option.
Hope that helps.
And : sorry for your loss!