I thought the same about the Home Educating at first icecream I was thinking it would be a real spanner in the works. But then if you think about it it another baby might actually be a huge help.
I am no expert on how the benefits system works but if she’s been out of work for a while and doesn’t have a very young child at home I’m guessing she’s under some pressure to look for at least part time work? Now her eldest is 20 she won’t get any CB, CTCs and I think possibly a reduced amount of HB? There won’t be any maintenance from the father now either, if there ever was any.
If the DD has moved out or is planning to, she could possibly be in a bedroom tax situation too. Or if the DD herself was PG the council may not consider her a priority for housing if her mother can adequately house her and a baby. If the OP can argue that she is overcrowded with a new baby of her own then it changes things.
So if she has another baby then she is back to where she was in terms of arguing that she’s not able to work for another 5 years, back to higher levels of HB and CB and in need of that extra bedroom again. Therefore free to to home Ed her DD without losing out financially whereas working part time or fulll time would make that impossible, plus the potential for childcare costs.
If her first DD had been younger, under the new system she’d not get any more money for a subsequent 3rd child, but now the DD is over 18 I believe she will? I think it’s not the amount of DC you have but the amount all under 18 at the same time? I might be wrong though - as I said, I’m no expert.
Obviously I have no idea which if any of these scenarios might apply to the OP and she could own her house and be entirely self funding for all we know. But I can think of several hypothetical situations where an accidental PG for someone in the OPs situation might actually be quite fortuitous in the long run.
It’s also possible that the new chap is loaded so any maintenance awarded could be pretty high. Then again he could be one of those 5 quid a week dads.