Unknown mistress of Louis I - Not Theodelinde of Sens

The wikipedia source for Arnoulf https://en.wikipedia.org/wiki/Arnulf_of_Sens doesn't cite the primary documentation, and even wikipedia finds this suspicious. The assumption appears to be based only on Arnoulf's being made Count of Sens by his father

Arnulf of Sens
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Arnulf of Sens (c.794 – April, 841) was a Frankish noble, an illegitimate son of the Louis the Pious,[1] son of Charlemagne. He had one sister, Alpaïs de Paris,[1] abbess of St-Pierre de Reims. In 794 Arnulf's mother Theodelinde of Sens died. His grandfather Charlemagne died in 814, and Arnulf's father Louis became Emperor. Three years later in 817, Arnulf, was appointed count of Sens in Burgundy. He was the first son of Louis the Pious, but he did not inherit land because his birth was illegitimate. In April 841, a year after his father had died, he died at Sens.

References
McKitterick 2008, p. 93.
Sources
McKitterick, Rosamond (2008). Charlemagne: The Formation of a European Identity. Cambridge University Press.

Find A Grave, though, seems to have a Theodelinde de Sens and her (purported) father Gainfroi de Sens both buried at Abbey de Sainte Colombe de SensSens, Departement de l'Yonne, Bourgogne, France
https://www.findagrave.com/memorial/147277593/theodelinde-de_sens

But her purported mother Theidlindis de Blois de Sens is not buried there (or anywhere known) - somewhat surprising.

The only child that Find A Grave gives as Theodelinde's is Alpaïs d'Aquitaine - not buried with her purported mother (not surprising, though.)

Arnoulf's grave or relationship to Louis is unmentioned by Find a Grave.

While geni cites no sources for Gisela of Lotharingia, Abbess of Nivelles or her purported father Reginmund van Friesland who is purported to be the other husband of Unknown Concubine of Louis I<

Primary sources suggest that Gisela, Abbess of Nivelles is the illegitimate child of Lothair

GISELA ([860/65]-[21 May/26 Oct] 907). Regino records the marriage in 882 of "Gisla filia Hlotharii" and "rex Godofridus Nordmannorum"[63]. The Annales Fuldenses record the marriage of "Gotafrid Nordmannus qui superiore anno fuerat baptizatus" and "Hugone Hlutharii filio eiusque sororem" in 883[64]. Abbess at Nivelles and Fosses, after her husband died. "Zendeboldus…rex" gave "proprietatem…in loco…VII Fontes" to "propinqua nostra…Kisla…regis Lotharii filia…abbatisse" by charter dated 30 Jul 896[65]. "Zuendebolchus…rex" gave property to "neptis nostre…Gissele…Nyuialensis abbaciæ" for her abbey by charter dated 26 Jul 897[66]. m (882) GODEFRID, son of HARALD "Klak" & his wife --- (-murdered Jun 885). He was one of the leaders of the Danes who ravaged large parts of territory between the Rhine and the Somme. He converted to Christianity, and Emperor Charles "le Gros" granted him large parts of Frisia as dux.

so I'm disconnecting these two from Theodelinde and Loius.

On the issue of using Find A Grave as a support for Unknown Concubine of Louis I as the Unknown mistress of Louis, it must be noted that Find A Grave's dates make Theodelinde 10! years old at the birth of Alpaïs, Abbess of St-Pierre & Reims
(the debate about whose paternity I have discussed at some length on the Charlemagne Descent line project: https://www.geni.com/projects/Charlemagne-Direct-Descent-Line/1550)

There is thus no evidence anywhere that I can see to make Theodelinde the mother of Alpais.

Thus no evidence I can find supports Theodelinde as the mistress of Louis and parent of either Arnoulf or Alpais - which is unsurprising as the medievalists appear to find none either.

New profile for Theodelinde, de Sens, daughter of Gainfroi, count of Sens and Theidlindis de Blois

Irmingard in de Haspengouw

Born circa 780

Died 3 October 818

Source : FamilySearch

States she was married to Louis I 'the Pious', and to Lodewijk I, Keizer der Franken en Kombarden

Not sure if this can shed some light.

No primary sources.