Toddler hitting rocky patch - how do I help her?

[Feierabend]

My 2.7 yr old DD seems to have hit a rocky patch over the past few days. After being pretty much fully potty trained since summer, she's gone back to constantly wetting herself. She wakes up at night and calls for help with finding her duvet / water (she doesn't normally wake up). Her favourite word is 'no' and when I played with her earlier, nothing I did or suggested was right, she went from one near tantrum to the other (she never has tantrums). At nursery they said she'd been unusually quiet all day and sucked her thumb a lot. I think it must be an insecurity thing, and I feel very sad for her, and wonder how I can help her be the positive, inquisitive girl that she normally is.

DD2 is 6 1/2 months old so I don't know if it can have anything to do with jealousy. DD1 has so far never had a problem with adjusting to changes in her life e.g. moving up to the next nursery group, and was always very good with her little sister.

Any ideas / encouragement (for me ) would be much appreciated.

She sounds very normal. I think regressing and progressing is all normal in the life of a toddler, no? And tantrums, waking at night, saying no- yep, ticks all those toddler boxes, even if she hasn't done it before. Sounds like you just need to ride it out, providing lots and lots of security and hugs and reassurance in the day. And not make too much of it yourself. She's going to change so much over time.

I found this book quite helpful, it's about understanding your toddler and her development from a psychological point of view:

understanding your toddler

and this

understanding toddler leaflet

Thank you so much, I'll have a look when DD2 lets me!