Question: Who did the woman disposed as regent by the King of Mercia married to?

Context paragraphs:
Ceolwulf II of Mercia: Ceolwulf II (died c. 879) was the last king of independent Mercia.  He succeeded Burgred of Mercia who was deposed by the Vikings in 874.  His reign is generally dated 874 to 879 based on a Mercian regnal list which gives him a reign of five years.  However, D. P. Kirby argues that he probably reigned into the early 880s.  By 883, he had been replaced by Æthelred, Lord of the Mercians, who became ruler of Mercia under the lordship of Alfred the Great, king of Wessex.

Wulfhere of Mercia: Wulfhere or Wulfar (died 675) was King of Mercia from 658 until 675 AD.  He was the first Christian king of all of Mercia, though it is not known when or how he converted from Anglo-Saxon paganism.  His accession marked the end of Oswiu of Northumbria's overlordship of southern England, and Wulfhere extended his influence over much of that region.  His campaigns against the West Saxons led to Mercian control of much of the Thames valley.  He conquered the Isle of Wight and the Meon valley and gave them to King Æthelwealh of the South Saxons.  He also had influence in Surrey, Essex, and Kent.  He married Eormenhild, the daughter of King Eorcenberht of Kent.

Sighere of Essex: Sighere was the joint king of the Kingdom of Essex along with his cousin Sæbbi from 663/4 to about 688.  He was son of Sigeberht Sæwarding, probably Saint Sigeberht, but perhaps Sigeberht the Little.  He was outlived by Sæbbi, who became the sole ruler of Essex after his death.  Sighere and Sæbbi were cousins of their predecessor Swithelm.  While Sighere returned to paganism, Sæbbi remained Christian.  They soon developed a rivalry.  Sighere found an ally in Wessex, and Sæbbi with Mercia.  As a result of their rivalry, King Wulfhere of Mercia established himself as overlord of Essex.  and induced Sighere to marry his niece Osgyth, daughter of Frithuwold, sub-king of Mercia in Surrey.  Jaruman, the bishop of Mercia, was assigned to reconvert the people of Essex to Christianity.  In 673, Sighere separated from Osgyth, who then fled to the protection of Bishop Beaduwine of North Elmham.  Sighere died about 688, and Sæbbi became sole ruler of Essex.

Wiglaf of Mercia: Wiglaf (died 839) was King of Mercia from 827 to 829 and again from 830 until his death.  His ancestry is uncertain: the 820s were a period of dynastic conflict within Mercia and the genealogy of several of the kings of this time is unknown.  Wigstan, his grandson, was later recorded as a descendant of Penda of Mercia, so it is possible that Wiglaf was descended from Penda, one of the most powerful seventh-century kings of Mercia.

Æthelflæd: Æthelflæd, Lady of the Mercians ( 870 - 12 June 918) ruled Mercia in the English Midlands from 911 until her death.  She was the eldest daughter of Alfred the Great, king of the Anglo-Saxon kingdom of Wessex, and his wife Ealhswith.  Æthelflæd was born around 870 at the height of the Viking invasions of England.  By 878 most of England was under Danish Viking rule, East Anglia and Northumbria having been conquered and Mercia partitioned between the English and the Vikings, but in that year Alfred won a crucial victory at the Battle of Edington.  Soon afterwards the English-controlled western half of Mercia came under the rule of Æthelred, Lord of the Mercians, who accepted Alfred's overlordship.  Alfred adopted the title King of the English, claiming to rule all English people not living in areas under Viking control.  In the mid-880s, Alfred sealed the strategic alliance between the surviving English kingdoms by marrying Æthelflæd to Æthelred.

Æthelred of Mercia: Æthelred ( ; died after 704) was King of Mercia from 675 until 704.  He was the son of Penda of Mercia and came to the throne in 675, when his brother, Wulfhere of Mercia, died.  Within a year of his accession he invaded Kent, where his armies destroyed the city of Rochester.  In 679 he defeated his brother-in-law, Ecgfrith of Northumbria, at the Battle of the Trent: the battle was a major setback for the Northumbrians, and effectively ended their military involvement in English affairs south of the Humber.  It also permanently returned the kingdom of Lindsey to Mercia's possession.  However, Æthelred was unable to re-establish his predecessors' domination of southern Britain.

Cynethryth: Cynethryth ("Cyneðryð"; died after AD 798) was a Queen of Mercia and wife of King Offa of Mercia and mother of King Ecgfrith of Mercia.  Cynethryth is the only Anglo-Saxon Queen consort in whose name coinage was definitely issued.

Ælfflæd of Mercia (II): Ælfflæd (fl.  840), was the daughter of Ceolwulf I of Mercia, and later married Wigmund of Mercia.  Their son, Wigstan of Mercia, inherited the throne in 840 but, declining the kingship, appointed his mother as regent.  She was deposed from this position by Beorhtwulf of Mercia.  Ælfflæd should not be confused with her earlier Mercian namesake, Ælfflæd, the daughter of Offa of Mercia.

Æthelred, Lord of the Mercians: Æthelred, Lord of the Mercians (or Ealdorman Æthelred of Mercia; died 911) became ruler of English Mercia shortly after the death of its last king, Ceolwulf II in 879.  His rule was confined to the western half, as eastern Mercia was then part of the Viking-ruled Danelaw.  Æthelred's ancestry is unknown.  He was probably the leader of an unsuccessful Mercian invasion of Wales in 881, and soon afterwards he acknowledged the lordship of King Alfred the Great of Wessex.  The alliance was cemented by the marriage of Æthelred to Alfred's daughter Æthelflæd.

Beorhtwulf of Mercia: Beorhtwulf (] , meaning "bright wolf"; also spelled "Berhtwulf"; died 852) was King of Mercia, a kingdom of Anglo-Saxon England, from 839 or 840 to 852.  His ancestry is unknown, though he may have been connected to Beornwulf, who ruled Mercia in the 820s.  Almost no coins were issued by Beorhtwulf's predecessor, Wiglaf, but a Mercian coinage was restarted by Beorhtwulf early in his reign, initially with strong similarities to the coins of Æthelwulf of Wessex, and later with independent designs.  The Vikings attacked within a year or two of Beorhtwulf's accession: the province of Lindsey was raided in 841, and London, a key centre of Mercian commerce, was attacked the following year.  Another Viking assault on London in 851 "put Beorhtwulf to flight", according to the "Anglo-Saxon Chronicle"; the Vikings were subsequently defeated by Æthelwulf.  This raid may have had a significant economic impact on Mercia, as London coinage is much reduced after 851.

Supporting paragraphs: Ælfflæd of Mercia (II) Beorhtwulf of Mercia
Answer: Wigmund of Mercia