Plus why then would she be granted DLR when they moved to the UK?
Because she didn't apply for a spouse visa I assume.
It reads like she entered on a visitor visa with her 3 British children. DL was quite easy to get if she then refused to leave the UK at the end of her visitor visa, as she then claims EU laws Human Rights to be able to stay in the UK (as her 3 young British children live in the UK). Back then, she would have had access to Legal Aid to use a solicitor for free. Her children won't be deported (as the Daily Fail claims) as they are British.
Once she got DL for 3 years, it should have just been a case of applying for another DL for 3 years (which she would have got if her circumstances hadn't changed - which they haven't as she is still married and her children live in the UK). Then after 6 years on DL, she could have applied for ILR.
Has she tried to apply for ILR instead of another DL? Or let her DL expire? If it expired then she will have to apply for the new 10 year route (as she has British children) until she has 10 years of unbroken legal stay, to get ILR. She will now have to fund her own legal bill.
DL to stay in the UK, has been removed and the new 10 year rule brought in, to make it fairer to the immigrants who do follow immigration rules to ILR.
It would have all been over by by now if she had just applied for a settlement visa instead of going the DL (outside of UK immigration rules) route.