My mother-in-law recently died and her house was part of her estate. The house was sold and the money from it taxed in the U.K. (Wales). My wife is a partial beneficiary, and her share (over 100,000 U.S.D.) is ready to be shipped. Can we protect this money from taxation here in the U.S. by investing in any kind of account? Approximately how much would the tax be (Federal as well as state tax (Maryland)?

In the U.S. any money or property you inherit is not taxable. So the share your wife gets is not taxable in the U.S.
For more information read: Your U.S. Tax Return: Tax on Inheritances

However, IRS will want to make sure that money you are getting is gift or inheritance from abroad. If the amount you are bringing to the U.S. exceeds Rs. 100,000 you must file Form 3520: Notice of Large Gifts Received from Foreign Persons. It is only for reporting; there is no tax liability.

Agreed; the inheritance can be received tax-free.

You just need to report the receipt of the money to the IRS.

If you can show that the money is in fact an inheritance, you should have no problems.

And if you have an interest in a U.K. bank account, then you should file Form TD F 90-22.1.

A U.S. citizen or resident must report worldwide income including foreign bank interest.

United States Treasury Regulation 31 CFR 103 require that every United States person file this form TD F 90-22.1 if at any time during 2006, you have an interest in or a signature or other authority over a financial account in a foreign country, such as a bank account, securities account, or other financial account and the total amount at any time in the year was $10,000 or more.
Read: Mandatory Reporting of Foreign Bank and Financial Accounts