K.G.
well, it seems you know what you are doing! I think that yes, it has a lot to do with having an infant at home. Psychologically she feels she has been "replaced" as the baby in the family....it is common for kids to regress, to go back to immature behaviors; even ones that are already trained can suddenly start having accidents again. You can either wait a few months, then try again, or try to spend some alone time with your daughter, not related to potty training, where you are giving her your undivided attention. Praise her a lot when she acts like a big girl in other ways...like for example, helps you feed the baby or goes to preschool or does an activity of her own...maybe even together with the 5 year old. If she feels secure in her role in the family, but not "pressured" to grow up, she will come to see the benefits of being a big girl, and this will motivate her to WANT to potty train. My kids were 23 months apart and we didn't even try to train my daughter until she was almost 3, because all the books say not to do it at the same time you have an infant come into the home. God bless you! I don't know how you do it....raising 2 was hard enough for me. I always wanted a big family but almost died giving birth to my son, who was a twin with twin-twin transfusion syndrome (the other baby died). My husband was afraid to try again after that. Anyway, I am sure things will work out for you because experience is the best teacher! I'm just telling you what i know from the "book-smart" point of view.