I think that her LNAB may be incorrect but I think that if you agree about that then it might be necessary to get a leader to change it.
The book that is supposed still to be the reference for the family history (though needs scrutiny) uses the surname Bevil(l). They were a family from Gwarnock and apparently intermarried with the Grenvilles several times. There is a Sir Bevill Grenville, a Royalist who died in 1643 which would appear to add some confirmation to this.
The will of her grandfather is quoted in the book, this was written in 1515,.In it he gives £20 to Matilda Grennefeld , daughter of his son John Bevyll .
If the account of her death is to be believed, both she and he died from hardships endured during their capture at Trematon castle in 1549 during the Prayer Book Rebellion . Her date of death is given as 25 April 1551. (buried in Kilkhampton) The story of their capture comes from Carew bk2 p 111 but this does not state that their deaths were as a result of ill health caused by the incident (deaths aren't mentioned)
I haven't been able to find anything to confirm that death (not found mention of a memorial in the church and the registers don't seem to start that early) As she was left land Buckland Abbey for 70 years or until her death, there might be something there to be found.
See History of the Granville Family p 81, 82, 128
and D and J Carter: Grenville Research, (report produced to accompany the Historical Research and Statement of Significance Reports into Nos. 1 to 5 Bridge Street, Bideford )http://www.nimrodresearch.co.uk/grenville/pdf/Grenville%20research.pdf
(there are some dates in the above document and a full transcript of her husbands will and a summary of his IPM. edit will transcript actually from above book, not in National Archives, but if probated in Exeter would as suggested have been lost in the war)
I will add what I found about her if David hasn't found and entered it. (it doesn't help working in different time zones!0
