St Quintin to 2nd creation of Herbert earls of Pembroke

In CP Vol XI, p. 368, on Saint Quintin, an account of a Herbert St
Quentin who d. in Feb 1301/2 ends with, in note (c):

"Holding Stanton Quintin, Wilts and Stanton Quintin, Dorset, or the
earl of Gloucester... His heir Herbert, s & h. of his s. Herbert,
was then aged 17 or 18 (Cal. Inq. p. m. vol iv, no 153). He d.
shortly before 7 Feb 1338/9 (Cal. Fine Rolls, vol v. p. 115). His s.
and h. Herbert fought at Crecy, and d. in May 1347, leaving Elizabeth,
aet. 6-7, and Lora, aet. 5, his daughters and heirs (Cal. Inq. p. m.
vol ix, no 45). Elizabeth d.s.p. and the descendants of Lora, the
Herbert Earls of Pembroke of the 2nd creation (1551) styled
themselves Lords St Quintin on the ground of the descent."

I think this Lora has to be the same as the Lora, dau of Herbert St
Quintin who m. Sir Robert Grey and had a dau. Elizabeth who m. Henry
FitzHugh, 4th baron FitzHugh (CP V, 424). She also gets a mention in
the Marmion article, CP VIII, 522.

Between pp. 435 and 436 or CP Vol V is a pedigree of the FitzHugh lords
of Ravensworth. It shows that the Fitz-Hugh co-heirs included Elizabeth
FitzHugh (d. bef 1507) who married Sir William Parr KG (1434-1484).
Elizabeth and William Parr's eldest s. Thomas (d. 1517) had at least
one s. and two daus, Katherine, last queen to H. VIII, and Anne who
married William Herbert, (c.1506-1569/70) first earl of the new 1551
creation; the second earl came from this marriage.

So the line from Lora to the second earl is:

Lora St Quintin = Sir Robert de Gray (d. bef 1367)
|
Elizabeth de Grey (d. bef 1427) = Henry FitzHugh (c. 1358-1425)
|
William FitzHugh (d. 1452) = Margery Willoughby (d. bef 1452)
|
Henry FitzHugh (c. 1429-1472) = Alice Neville (d. aft 1503)
|
Elizabeth FitzHugh (d. bef 1507) = William Parr (1434-1484)
|
Thomas Parr (d. 1517+ = Maud Green (c. 1495-1531)
|
Anne Parr (d. 1521/2) = William Herbert (c.1506-1570)
|
William Herbert (aft 1538-1600/1)

From this, the second earl was indeed descended from the St Quintins,
but I can't see how the first earl was so descended. Has anyone got any
better ideas?