It is certainly possible that sudden onset bedwetting after a long period dry was triggered by something, but given all the pressures you are under with three kids 6 and under, I wouldn't be too worried that something really weird happened -- certainly it's worth checking with the school counselor's perceptions and checking to see if you can put anything together, but it sounds like with so many young children in a blended family, everyone is under a lot of stress and that this may be coming out in this way. The good news is that a lot of this is about a steep, steep learning curve for everyone and it won't be this hard forever, or even for all that long. My 7 year old has ADHD and a grandmother who wet the bed until she was 11, and to me it makes sense that she struggles with on-gain, off-again bedwetting that kind of crops up whenever the family is under stress. I have found the "electric underpants" that are sold on line -- underpants with an alarm that notes wetness -- to be very, very helpful, but they are expensive and I feel they work great if the kid is eager to fix the problem and not at all well if the kid isn't the one eager to get dry. There are so many issues that can connect to this, heavy sleeping, small bladder, anxiety, genetics, and sure, of course, attention deficit or it's cousin, sensory integration disorder, both would make it harder tor a child to register their body's signals. I've really torn my hair out about this at times, but every time I check it out in any source, it says that in each year about 10 percent of kids with bedwetting will outgrow it naturally. I love my daughter enough to give her a tool when she herself is feeling ready to stop, but other than that, I praise her when she makes it through dry and keep a plastic sheet on the bed no matter where she is in the cycle (dry for a couple months now, so, yay!!)
good luck!
M.