Ingeborg Yngvasdotter - dotter of Yngve Alreksson ?

There's a link in her husband's profile: http://www.vulkaner.no/f/m7xfm5xfp.htm - indicating that we have to look at the Denmark-focused sagas for the source (if any).

Some sagas to search here: https://en.wikipedia.org/wiki/Fr%C3%B3%C3%B0i

"FRODE DEN 3., DEN FREDSSAMME (FREDELIGE)
Frode efterfulgte sin fader Dan den 2.; han var født til fred, ikke til våben. Han giftede sig med Inga, datter af Sveriges konge Yngve Alrikssøn, som er den 14. Konge i den svenske kongerække, eller den 17. Efter nogles beregninger. Da Frode på en jagt havde indhentet en hjort og gennemborede den med sit spyd, fik han mave og indvolde revet op af hjortens gevir, da den vendte sig imod ham, og han faldt død om; han blev begravet på Sjælland. Han havde med sin hustru Inga sønnerne Fredleif og Halfdan."

Vulkaner.n is a private page - no source mentioned "efter nogles beregningar."

In the notes about Frode Dansson a source for Ingibjorg is asked for:

"Basics: Father: Dan "the proud" Olavsson Mother: Olof Vermundardotter (according to "Hvorledes Norge Byggdest) Wife: Inga or Ingibjorg Yngvesdotter (source needed) Son: Halfdan Frodesson Son: Fridleif Frodesson Sources"

The relationship between the Uppsala kings and the kings of Lejre in Danmark is known through the marriage of Yrsa and Adil.
"Leijre in Zealand is a royal manor belonging to the Sköldung dynasty, founded by Sköld, son of Odin. Adils, king of Uppsala has married into the family.
The royal manor of Leijre has the same significance and function as its Uppsala counterpart, but Lejre does not become so famous." That is what the Old Uppsala museum has presented.

Adil and Yrsa are many generations (4 or 5) later than Frodi and Ingeborg. Scholars at the Uppsala museum would have mentioned the relationship between Uppsala and Lejre if there would be a source for Frodi and Ingeborg, "dotter" of Yngve Alreksson. Frodi belongs to the Lejre clan - the Skjøldingar - clan.

I believe that Ingeborg is fabricated but I will have look into Skjøld - sagas.

In the notes of Ingeborg there is the link "The Skjoldungs".

http://talbotsfineaccessories.com/genealogy/skjoldungs.html

Another private link without Ingeborg but including Adil and Yrsa.

If I were to guess, I'd bet on Sogubrot (seems to be what's left of Skjols saga) or Gesta Danorum.

The "efter nogles beregninger" refers specifically to whether Yngve was the 14th or the 17th Swedish king (both numbers seem too large). The whole paragraph is obviously a quote (language is archaic Norwegian/Danish), but it doesn't say from where.