Like most Devon wills this one did not survive the bombing of Exeter in 1942, but fortunately we have Miss Oliver Moger to thank for extracting the main contents before the war.
This abstract is in vol. 1 of Miss Moger’s will abstract, p.163-4; the volumes are held at the DHC.
Miss Moger’s absract (comments in square brackets and use of bold are my additions; bold indicates related / connected through her husband, non-bold links are Jane’s own relations):
Ballamy, Jane, of Woodford in Blackawton, widow.
Date of Will [i.e. date written] 23 Sept. 28 Geo. III. 1788.
Proved 18 Oct. 1788 by John Prowse, executor.
To niece Ann Rich [daughter of her husband’s sister Dorothy] wife of William Rich of Dartmouth,* mariner £50 and to her 2 children Ann Rich and William R. £5, and to said William, my late husband’s silver cratch [watch?].
To Dorothy Gunn [her husband’s sister] mother of said Ann Rich £10. 
To my niece Jane Ching of Slapton wid. £50.
To my sister in law Mary Harris wid. £10.
To Richard Ferris of Modbury, husbandmen £50 and 6 silver teaspoons marked I B.
To my brother in law William Bellamy [her husband’s brother] £20.
To my nephew John Roope [son of her husband’s sister Rebecca]. of John R. the younger of Woodford, woolcomber £10.
To Ann Hawkins [mother of her husband’s brother John’s reputed daughter] of Woodford spinster £6 and to her daughter Ann Hawkins [her husband’s brother John’s reputed daughter] £10, my clock and gold ring etc. 
To my kinswomen Mary wife of Nicholas Ryder of Dartmouth tayler [daughter of her husband’s sister Mary], Ann Hamlyn wife of James H. of Blackawton, blacksmith [daughter of her husband’s sister Mary], Sarah Tell wife of Geo. Tall of Blackawton, mariner [daughter of her husband’s sister Mary] and Elizabeth wife of John Weeks of Sherford, carpenter [daughter of her husband’s sister Thomasin] 2 guineas each.
To my nephew John Gunn [son of her husband’s sister Dorothy] £10.
To my godson Samuel Lambell s. of John L. of Blackawton, blacksmith.
To my niece Mary Ching of Sherford [daughter of her husband’s sister Thomasin], spinster 10s 6d.
To Thomas Harris Prowse s. of John Prowse of E. Allington yeoman £50 at 21.
Residue to said John Prowse, executor.
Seal a thistle
Witnesses: Mary Jellard, Walt. Prideaux, juniro.
(*inter lined over Kingwear deleted)
Not only are the bequests to a mix of Jane’s relations and her late husband’s, but she seems to sometimes refer to Matthew’s relations as though hers, sometimes as in-laws. Although it is possible that Jane and Matthew were relations before they married and so had nephews and nieces in common, referring to in-laws with nothing to show they weren’t blood relations is common in older wills (and other documents), and I think that is probably all that is happening here. When Jane uses ‘in law’ it is to refer to her husband’s siblings, when she omits it it is to refer to his nephews and nieces. Some nieces she refers to simply as ‘kinswomen’.
 Of her husband’s relations, it is his sister Dorothy and her children and grandchildren who receive the largest bequests. This probably means that it was this part of his family that she was closest to, but could be because of a second link – maybe they were her blood relations too, though we might have expected a reference to such a relationship and there is none.
 When Jane’s brother-in-law John Bellamy wrote his will, about five years earlier, he referred to Ann (the younger) as living with Jane; I guess this created a fondness of Jane for Ann that led to her leaving her her clock and ring etc., one of the few bequests that was not just monetary.