I strongly agree with the conclusion of the Google Group Gen Medieval discussion group in 2010 that Bertha/Berta de Braose was the wife of William Beauchamp who died about 1197, and was NOT the wife of William de Beauchamp who died about 1170. https://groups.google.com/g/soc.genealogy.medieval/c/g-Z_12VnIxw/m/Ul7pMbcjKSEJ
My analysis that leads me to this conclusion is as follows:
Follow the proven ownership of the manor of Tetbury. According to an article on the Manor of Tetbury at British History Online, the manor of Tetbury came into the ownership of the de St. Valery family with Reynold de St. Valery owning it about 1148. Reynold/Renold de St. Valery died about 1066 at which time it came into the ownership of his son, Bernard de St. Valery who died in 1197. Then Tetbury was granted to William de Breuse (it is speculated to be either upon or because of his marriage to Maud de St. Valery, daughter of Bernard). This William de Breuse/Braose was William de Braose (born about 1150; died about 1211), [not his father William de Braose (born about 1112, died about 1192) who married Bertha of Hereford]. Tetbury was conficated from William de Breuse in 1208 due to his quarrel with King John. Tetbury was then granted to Peter FitzHerbert in 1212. After William de Breuse/Braose's death in 1211, his heirs disputed ownership of Tetbury with the King. By 1215 the ownership of Tetbury was with Giles de Breuse, son of William de Breuse.
https://www.british-history.ac.uk/vch/glos/vol11/pp264-269
In supplement to the above account of Tetbury there is the Inquisition apparently following the death of John de Thorndon in 1305 (19 June 33 Edward I) which involves the ownership of Tettebury and other property. It says that William de Breouse, long since deceased, held the manor of Tettebury of the King in chief by the service of a knight's fee and he gave the rent "a hundred and sixty years and more past to William de Bello Campo, great grandfather of the said Earl [i.e., William de Bello Campo, the grantor of Tetbury to John de Thorndon] and Berta, daughter of said William de Brewose, in free marriage."
https://babel.hathitrust.org/cgi/pt?id=pst.000023992122&view=1up&seq=554&skin=2021
So, sometime during William de Braose's ownership he granted the "rent" from Tetbury to William de Bello Campo and Berta, his wife, daughter of said William de Braose. Since the land did not come into the ownership of the de Braose family until 1097 or after, the William de Bello Campo/Beauchamp who received the land from William de Braose on his marriage to Berta/Bertha de Braose could not have been the William de Bello Campo/Beauchamp who died in 1170), and thus must have been his son, William de Beauchamp who died about 1097.
The above inquest records was quite likely inaccurate to say that this William de Braose who granted the rent to William de Bello Campo was 160 or more years before 1305 (rather than lesser time). This is only me speculating, but perhaps the "160 years" was a confusion by the person taking the inquest with the earlier ownership of Tetbury in the de St. Valery family.