Her dad died before the Battle of Flodden (09 Sep 1513). So even if she was born that same year, it implies she suddenly started having kids at the ripe old (menopausal) age of 59.
In any case, it's a good thing that the actions of her son Sir John Forster, were well-documented. Although the year of his birth is unknown, it's been estimated around 1520 -- seven years before his father died.
But more importantly, the battles he fought prove that there is NO WAY Dorothy married his father in 1572. For instance ... by November of 1542, John was engaged in the Battle of Solway Moss. And five years later, he was knighted.
There are also conflicting sources when it comes to identifying Dorothy's second husband. Burke (1831), states he's John Grey of Horton, while Parliament, and Ogle (1902) say he's Sir Thomas Grey of Horton (ante.1512 - 05 Aug 1570), who served as Marshall of Berwick. But Burke (1833), later agrees that she married Thomas Grey of Horton, so there was a publishing error at some point.
In any case, Ogle, (1902) is the authority for Ogle genealogy. He states there is no way Dorothy could be the daughter of Robert, 5th Baron Ogle, and that her father is Ralph, 3rd Baron Ogle. Evidence for Thomas Grey is further supported in the will of Dorothy's daughter, Dame Isabell Grey of Ogle Castle.
Father: Ralph, 3rd Baron of Ogle (b. abt.1468 - d. Jan 1513)
Mother: Margaret (living 16 Jul 1516), dau. of Sir William Gascoigne and Margaret Percy.
Margery (will 03 Nov 1612, proved: 19 Mar 1613/4)
m. John, son of George Heron of Chipchase and Marion Swinburne
Americana, (1920). (Vol. 14). NY: Publishing Society of New York. Google Books.
Bateson, E. (1893). "Forster of Adderstone," in a History of Northumberland, 1, pp. 228. Google Books.
Bethan, W. (n.d.) The Baronetage of England, 4, p. 34
Brooks, D.J.B. (2016). Tales of Northumberland Ogles: Their kith and kin. The Ogle Genealogist, 37, pp. 14-24. OOFA. Print.
Burke, J. (1831). A general and heraldic dictionary of the peerages of England, Ireland, and Scotland, extinct, dormant, and in abeyance. England. Google Books.
Burke, J. (1833). The portrait gallery of distinguished females: including beauties of the courts of George IV and William IV. E. Bull. Google eBook
Collins, A. (1720). The Baronettage of England, 2, pp.120 - 121. London: W. Taylor. Google Books.
Ellis, S.G. (2009). "Region and Frontier in the English State: The English Far North, 1296-1603." Frontiers, Regions and Identities in Europe. Cliohres. Pisa: Plus-Pisa University Press. Web. Accessed 13 Jan 2014. PDF. 
Flower, W. (1881). Visitations of Yorkshire 1563 and 1564. Charles Best Norcliffe, Ed. Harlein Society. Google Books.
Foster, J. (1871). A Pedigree of the Forsters and Fosters of the North of England and Some of the Families Connected with them. Archive.org. CAUTION!
Grey, Sir Thomas I (bef.1512-70), of Horton and Newstead, Northumb. and Bethnal Green, Mdx. HOP. Web.
Meikle, M.M. (2004). A British frontier?: Lairds and gentlemen in the Eastern Borders, 1540-1603. pp.338. Tuckwell. Google Books.
Ogle, H.A.(1902). Ogle and Bothal: History of the baronies of Ogle, Bothal, and Hepple, (pp.lxvii).
Raine, J. Greenwell, W., Hogdson, J.C. & Wood, H.M. (1860). "Wills and inventories from the registry at Durham part II." Wills and Inventories Illustrative of the History, Manners, Language, Statistics, &c. of the Northern Counties of England: From the Eleventh Century Downwards, (Vol.38, pp.). London: Mitchell and Son. Google eBook.
Citations and Notes
↑ 1.01.1 b. 1488/90; m. (1503/5) Thomas Forster (b. abt. 1466), (Brooks, 2016, p. 17).
↑ Dorothy's father was succeeded by his heir Robert before the Battle of Flodden on 09 Sept 1513. Her youngest son Sir John Ogle was probably born in 1520, so Dorothy is probably b. c. 1480/90s.
↑ 8.08.1 Foster, (1891) misidentified Dorothy's parents as Robert, 5th Baron of Ogle and Dorothy Widdrington (due to a typo in Glover's pedigree). While they did have a daughter named Margery ... she married Gregory Ogle of Choppington. The 5th baron's second wife also had a Margerye, but she married Robert Widdrington (p.859).
↑CAUTION: Pierce (1899), states Dorothy married Thomas Forster in 1572.That's WRONG! Wurts (1945), repeats the same error.