I think Ermengarde’s mother is supposed to be Adelaide of Burgundy
http://fmg.ac/Projects/MedLands/BURGUNDY.htm
RICHARD, son of comte BUVINUS [Bouvin] & his wife --- d'Arles (-[31 Aug or 1 or 29 Sep] 921, bur Abbaye de Sainte-Colombe de Sens, Yonne). …
m ([887/88]%29 ADELAIS, daughter of CONRAD Marquis of Transjurania [Welf] & his wife Waldrada --- (-after 14 Jul 929). …
Duke Richard & his wife had [four] children:
1. RODOLPHE [Raoul] (-Auxerre, Yonne 15/16 Jan 936, bur église de l'abbaye de Sainte-Colombe de Sens). Flodoard names "Rodulfo filio Richardi"[24]. …
2. [ERMENGARDE (-after 9 Dec 943). Ermengarde, wife of Giselbert, has been accepted as the daughter of Duke Richard since Du Chesne in 1625[42]. More recently this affiliation has been challenged, in particular because she is not mentioned in her supposed mother's will[43]. … m (before May 926) GISELBERT, son of MANASSES Comte de Vergy & his wife --- (-956). He became GISELBERT Duke of Burgundy, after Raoul and Hugues "le Noir" ceded him their rights to Burgundy in [936]. After his death, Lothaire King of France took direct control of his part of Burgundy[46].]
3. HUGUES "le Noir" (-17 Dec 952, bur Besançon).
4. BOSON (-Sep 935, bur Reims, église de l'abbaye de Saint-Rémi).
Duke Richard had one child [probably illegitimate] by [Mistress (1)]:
5. GEBUIN .
Who is Ermentrude of Alsace