She was born one of the three daughters of Richard Cecil (d 1553), by his wife Jane Heckington, daughter and heiress of William Heckington of Bourne, Lincolnshire. Margaret's mother Jane died in 10 March 1587/8. 
Margaret married first to Roger Cave (d Jul 25, 1586, son of Thomas Cave) and secondly to Erasmus Smith of Husbands Bosworth, Leicestershire.
- Elizabeth Cave (d 1638) m Walter Bagot of Blithfield (1557-1623)
- Frances Cave m Sir Edmund Bussey (son of John Bussey and Elizabeth)
- Thomas Cave m Eleanor St John
- Margaret Cave m Sir William Skipwith (1559-1610) of Cates, Leicestershire
- William Cave m Margaret
- Cecil Cave m Anne Bennett
- John Cave
- Anne Cave m Edward Bussey (is she confused with her sister Frances?)
- Dorothy Cave m Mr Hartopp
- The Visitations of the County of Oxford 1566, 1574, 1634 which States : "Sr Thom Cave, of Stanford, Kt. eldest son'e by his 2nd wife, maried Elizab. one of ye Daugh & heirs of John Danvers, of Waterstocke, Com Oxon. Esquir.... which Thom. Cave & Elizab. his wife had issue Rich. Cave, his eldest son'e, who had issue one daugh. maried to Edw. Gates, son'e & heire to Sr Hen. Gates, of Semar, com. Ebor., Knt.; Roger Cave, 2nd son'e; Edw. 3rd son'e ..."
- Gentleman's Magazine "In reply to Q p 197, I beg to say that in Nichol's Leicestershire, vol ii, p 184, there is a pedigree of Smith, alias Harris, of Withcote, co Leicester [Visitation by Sampson and Vincent 1619, continued by Sir Thomas Cave, Bart], agreeing in most particulars with two to be found in Harl. MSS. No 1080, fol 37b and 38, and No 1463, p 34, by which it would appear that John Smith, alias Harris, of Withcote, co Leic. who died 1546, married Dorothy, daughter of Richard Cave, of Stanford, co Northampton. Kimber, in his Baronetage, calls the husband of the said Dorothy, William Smith, alias Harris, of Witchcock in Leicestershire, esq. This is probably a mistake. Kimber, Baronetage, vol i, p 361. According to the aforesaid pedigrees of his descendents in the British Museum, besides nine other children, he had one called Erasmus Smith, of Bosworth, placed in the 4th place, but called the third son in No 1080, and placed and called the fifth in No 1463, where Ambrose is in the 4th place; and another, Ambrose Smith of London, called the fourth son in No 1080. Erasmus is said to have married, as his 2nd wife, Margaret, sister to William Cicell, Lord Burghley, and widow of Roger Cave; while Ambrose Smith married Joane, daughter of John Cooe, of Coxall in Essex, by whom he had several children, one of whom was Dorothy, wife first to Benedict Barnham, Alderman of London, and afterwards to Sir John Packington."
- Cemetery Monument of her parents, which mentions her two marriages, but calling her second husband "Ambrose Smith"
- Her entry at Will Johnson's Royals
- Her entry at genealogics.org, citing Burke's Peerage (no publication year given), giving her one husband, Roger Cave of Stanford, and by him, five Cave children: Elizabeth, Frances, Margaret, William, and Thomas.
- Cecil family entry at tudorplace.com.ar giving her three husbands, including a second husband William Skipworth, states that she was born 1523 without citation, and giving her one child Elizabeth
- Her entry at thepeerage.com, citing Burke's Peerage 106th (1999) and 107th (2003) editions, giving her one husband Roger Cave by which five children: Elizabeth, Frances, Margaret, William, and Thomas.
- Cecil01 at stirnet.com, giving her one husband Roger Cave. Cave02 at stirnet.com giving them seven children: Thomas, Cecil, Elizabeth, Margaret, Frances, William, John
- Her entry in the Ancestral File, AFN: B3L3-RR showing two husbands, but no children.