Oddly enough, she is a Countess. The Anglo-Saxon word Jarl was used in England to replace the Latin Comes - Comte in French, Count in English. The Comes was the head of a Comitatis - modern County. Under the Norman Conquest, the Earl became a local ruler, but his wife was described in Norman French, hence Countess.
In the British nobility, a viscount is ranked immediately above a baron and immediately below an earl. I doubt whether a viscount would "serve under an earl" as you put it.
earl
The French Vampire, Viscount de Morieve, lived during the French Revolution, if legend is correct, and for nearly a hundred years after that, before his grandson had him staked.
Viscount is a title held by certain British noblemen, and ranks below an earl and above a baron. The first person to be titled a viscount was John Beaumont, who received the honor in 1440. Today the title is usually given to men whome the ruler wishes to honor.
duchess
The gender noun of "viscount" is "viscountess." While "viscount" refers to a male holder of the title, "viscountess" refers to a female holder of the title, typically the wife of a viscount or a woman who holds the title in her own right.
The wife of a viscount holds the title of "Viscountess." This title is used in the British peerage system and is typically accompanied by the wife’s first name, such as "Viscountess Jane." If a viscountess has her own title in the peerage, she may also be referred to by that title.
A duke is addressed as "Your Grace," while their spouse is referred to as "Duchess." An earl is addressed as "Lord" and his spouse as "Lady." A viscount is addressed as "Lord" with "Lady" for his wife, and a baron is also "Lord," with their spouse similarly called "Lady." A marquess is addressed as "Lord" and his wife as "Marchioness."
The son of a viscount is typically referred to as a "courtesy title," specifically "the Honourable" or simply "Hon." followed by their name. However, he does not inherit the title of viscount unless he becomes the viscount himself. The specific title can vary based on the customs of different countries and peerage systems.
A vicomtesse - note the spelling - is the wife or widow of a vicomte. That's the French versions. In English we talk of a viscount (the male) and viscountess, h is wife or widow.
The wife or widow of an earl or count; a member of the British peerage ranking below a marquess and above a viscount
The wife or widow of an earl or count; a member of the British peerage ranking below a marquess and above a viscount
Marcy Stewart has written: 'Charity's gambit' 'The Viscount Takes A Wife' 'The bridegroom and the baby'
Viscount Exmouth was created in 1816.
Viscount Palmerston was created in 1723.
Viscount Bangor was created in 1781.
Viscount Scarsdale was created in 1636.