I think Feebs has got major anger issues and the kids are on the receiving end. She loves it when they are babies and small toddlers, then the anger has appeared as the kids have grown, I don't think she can cope.
She came on her stories to offload about Herbie due to the guilt bothering her. She even did a little laugh when she said "a little upset Herbie again", right when she was saying "again", it as a bit of a weird nervous laugh, so it sounds like Herbie being upset due to Feebs is the norm or a regular occurance. I think in the heat of the moment it is a snap reaction and it's only when she calms down and reflects she realises what she is like. It will be a tough cycle to break as I expect it's a mothering trait of hers now.
I mean we all have bad days, days when we are tired, chores are mounting up, the kids aren't listening and then we end up sounding like we're at our wits end. However I think for Feebs is a regular occurrence. This is why she is out so much with them, so she has head space and doesn't have to play with them.
She needs to start looking after herself to get her mind sorted. It's a good thing she has signed with that dietician because they're reminding her of the basics, to get more sleep, stop drinking alcohol so much, get the steps in, take her meds... All those things will help her anger issues.
It's almost like she has two personalities, the one the kids and Jim sees. Then her friends and Instagram personality. I bet she doesn't admit her faults to Jim, just to the whole world instead.