Raven has held off on marrying Wanderer for a few reasons, chiefly because she knows that she is a target and she doesn't want her enemies to go after her family in order to get at her. If it came to the worst, she thinks that she could convince Wanderer to hit the backcountry and disappear; as a former traveling bard, he's used to being on the road and getting by with very little. She herself could either go with him or stand and fight, depending on the odds. Either course of action would be nearly impossible if she were pregnant or nursing.
In the Starchild timeline, Raven was going to marry Wanderer after Lothanas Alarun and his allies were exposed and removed from power. In the modified timeline, if Merai is corrupted by Suspira and manipulates the Emperor into executing Alarun and putting her in his place, Raven will be stuck in a place of uncertainty. Merai is outwardly a friend to Raven and the Metamor Lightbringers, and will likely be busy rooting out Ba'al's servants within the Order as she works to bring about Suspira's planned takeover. But Raven will know that the prophecy isn't unfolding as it was supposed to, and that will clue her in that something is wrong. In that context, she's likely to continue delaying her marriage to Wanderer until she gets to the bottom of what's really going on. I doubt she'll be at peace with starting a family until after Merai has been freed from Suspira's influence.