Grumpy daughter .Part 2

Just needed a little vent again.I posted a few months previously about feeling like a punch bag every time my DD is feeling tired and grumpy -whichever way too often given that she lives close and I help with childcare at least twice a week ,including very early starts.Well things improved a lot when she reduced her hours .It was unsustainable for them as a couple given her partners very long days and early starts too.They have at times a volatile relationship,and whilst at times I feel exasperated with him I'm not blind to her faults.And I began to relax and enjoy her company again,or even fell less anxious just discussing arrangements with her.Honestly any conversation however innocent had the potential to cause offence.
Well she's pregnant again.And whilst of course in one way I'm pleased and excited,as is DH,we also are worried about how she will cope and furthermore how it will impact on us.I simply can't go through all the snipiness again.My other DDs has seen and been on the receiving end of her moods.And we're all holding our breath for how things will go with baby no 2.She's a lovely capable mum,with many good points .And I hate feeling critical of her,because she's her own worst critic .I know she doesn't need judgement but support. But she does also get a lot of help,not just from DH and I but her sisters and compared to a lot of mum's struggling with nursery drop offs,full time work, poor housing had really she has a set up many would envy.
I know I need to count to 10+ and walk away.My others DDs have told me to help only when absolutely necessary,and not offer any more.I know from previous replies my experience is shared. Just looking for solidarity as I'm about to go round to collect her dog and can tell she's not had a good night with the little one and morning sickness.Help !