It could be argued that Gislebert came closer to implying Richilde was
legal heiress of Valenciennes (though I don't think it sustainable as a
"portrayal") when he wrote that "they [she and Herman] added
Valenciennes" to the honor of Hainaut. A count's wife would not usually
receive this level of billing in a late-12th-century narrative.
There is circumstantial evidence that Richilde behaved as virtual ruler
of Hainaut and Valenciennes in the lifetime of her first husband,
Herman. This was perhaps due to their respective personal character
rather than to legal standing - she may have been simply the more
masterful of the couple.
One possible partial explanation of her position consistent with the
little evidence we have, which surprisingly (as far as I know) has not
been put forward before - and which I emphasise is _not_ my own opinion
by a long stretch - is that Richilde may have been Herman's step-sister,
daughter by a prior husband of a second wife of his father Reginar V, a
lady named Hathuidis who was a potential heiress to Valenciennes.
Herman's mother was named as Mathilde by Jacques de Mayere in 1538, but
this does not appear in any extant earlier source. In the 1070s Sigebert
of Gembloux wrote that Herman's father Reginar had donated to his abbey
with his wife Hathuidis. In 1936 André Boutemy assumed that Hathuidis
was the correct name for Reginar's only wife, mother of Richilde's
husband Herman, but there is no compelling reason why Mathilde could not
have been the name of Herman's mother and Hathuidis a second wife of his
father, possibly the mother of Richilde.
Galbert of Bruges wrote that after the death of Richilde's second
husband Balduin VI of Flanders their son Arnulf stayed in his paternal
land around Cassel and Saint-Omer while his mother returned to Hainaut
and the environs of a mother ("Igitur cum Balduinus vir Richildis in
Brugis obiisset, filius ejus Arnoldus, cui patria pertinebat, cum mater
versus Montes et viciniam matris rediit, circa Casletum et Sanctum
Audomarum et illas partes conversabatur"). This text has usually been
considered problematic if not corrupt, but understood to mean that
Richilde returned to Mons and the environs of _her_ mother. These
environs presumably included Valenciennes, and if considered the
territory of Richilde's mother it may have been through her that the
hereditary right to Valenciennes was claimed. I think it more likely
that Galbert meant "vicinia matris" only in contrast to "patria", i.e.
the environs of Arnulf's mother as opposed to the lands of his father -
and possibly he actually wrote "vicinia materna" with 'er' represented
by the conventional horizontal mark that was too small or faint for a
copyist to notice and 'na' misread as 'rıs' ( the letter 'i' was not
normally dotted in his time). However, if following the translation
given most recently by Jeff Rider and by others before him, the mother
in question was Richilde's rather than Arnulf's.
In a different thread I will set out some chronological, relationship
and onomastic markers for seeking the elusive origin of Richilde, that
is among the most intriguing and intractable mysteries in medieval
genealogy.