Thanks, John. Bill Kent also posted a comment on John Harcourt's profile, and earlier today I replied there saying much the same thing, and drawing attention to problems with Matilda Harcourt’s profile, which lacks good sourcing and has a chronological impossibility - a son (profile unsourced) born in 1399 when she was said to be 66. The Magna Carta Project would indeed require much more reliable, if at all possible primary, sourcing before considering attaching Matilda as son of John Harcourt, and the difficulty with dates for her would need to be resolved. If she had a child born at the end of the 14th century, she cannot be John Harcourt’s daughter as John died in 1330.
I had a quick look on the web and found no reliable evidence for who were Matilda's parents. If anyone can find such evidence, it would be helpful to have it.