I think we can reliable state that they were both level 19 when they were raised.

We know there needs to be about 5 levels of strength difference for any significant deference between Aes Sedai. Merana's thoughts regarding Bera and Kiruna show us that this is about the point were weaker sister teeter between obedience and less specific deference. Level 14 to level 17 is enough for Bera/Kiruna to take control, but women of stronger personality can and do hold out (Felaana shows us this too), with only 3 levels difference. However just one more level down we see Kairen and Demira stay quiet and accept polite orders from Bera/Kiruna.

Now we can look at how Siuan clearly defers to Citalia who is a level 14 and can assume, given Siuans personality, there needs to be a fairly wide margin of strength difference for her to obey so readily. We also know from Moiraine that Duhara, if not for being Keeper, would need to defer to Moiraine. With Duhara placed at level 23 it seems natural that Duhara must be at least 4 levels below Moiraine for Moiraine to believe this.

Placing Moiraine and Siuan at level 19 works well for this and explains why Merean was enough stronger than Moiraine to defeat her rather easily, but still gives Moiraine and Siuan significant status when they were raised.