I thought it would be apparent from my post, I work in the field too - currently I manage a permanence team (children in care) and have previously worked as a social worker in the same, as well as as supervising social worker (assessing and supervising foster carers, including kinship)
There is more fostering training to do in the first year as there is foundational training, but foster carers are reviewed at panel every year and are expected to show that they are continuing to learn - the training requirement reduces but doesn't go away. They have to be available for regular supervision, that doesn't change, and the frequency would be led more by the children's needs and how much support the carer needs, not by how long they have been placed. Same with the child's reviews, care planning meetings, PEP meetings, childs social worker visits. It is a lot. Even if things are settled and can be reduced to the statutory minimum, it's a lot. And that's before we think about the actual caring role - if you think about it, it would be very unusual for a single parent of three children this age to be in a full time senior corporate job, and certainly not without a lot of help. As has been mentioned on the thread, children have been through trauma need more time and attention than most children, and the support usually can't be delegated out, because the children need their primary care giver. They are likely to need more appointments and services than other children.
I wouldn't expect anyone who hasn't fostered to know the ins and outs, just that I felt telling someone who has clearly been incredibly strong, and at risk of burning out, that they just need to 'lay down the law' with social services isn't helpful - it implies that they're in this situation because they're too soft, and that's really not the case. It could actually risk the placement eventually, if social services deem the OP isn't committed, and she's been very clear she doesn't want to lose the children to non related foster carers.
I know the situation is different but if someone were applying to be a foster carer (in a planned way rather than by circumstance as with kinship) they would be very unlikely to be approved if they were a single carer working full time, unless they had an unusually flexible job. It isn't because social services want to push people into poverty, it's because we know it's simply not sustainable and we don't want childrens placements to break down and them be moved again. I do know a handful of single kinship carers who work full time, but it's only possible because they essentially share the care with a extended family, eg in a situation where no one was able to commit fully but the family pulled together and kids are with an aunt, but grandad agreed from the off he'd do the school pick ups, or where someone works shifts and the kids have three nights a week at a different family members.
@SparklyLimeHair re being signed off, it would buy you some time - paid time - and hopefully give you a bit of headspace before making any major decisions. As much as I can understand wanting to just give notice tomorrow, you risk replacing one set of problems with another, eg if you've not had chance to work out the financials.