We submitted one to our local council in September last year. The statutory yellow sign appeared on the lamppost outside our house, with a closing date for objections in November. Then in November another sign appeared with an end date of late December.
We contacted our agents (architects) to ask what was going on, and the council came back to say that they'd missed their own deadline, so had to start again. They said they'd be in touch if they needed access for the site visit, and apologised.
Because of various personal distractions, and receiving the building regs approval twice, we failed to notice that approval hadn't been granted until I got an email asking to arrange access for the site visit - in May. The surveyor for that told me that he'd been employed specifically to clear up the council's backlog. Permission was finally granted in June.
So... if she's in Oxfordshire, she may also be stuck in the backlog. My advice to her would be to keep checking the application online, and don't take your eye off the ball like we did! If it's not clear why there's a delay, contact them, and try and pin them down to dates. That way if they miss a date, you can chase again. That might chivvy them along.
I think the fact is just that no one is moving house right now, and everyone is building extensions! If we'd had an easier time finding a builder, the delay would have been a nightmare, but as it is, most builders round here are booked up for so long that they wouldn't even quote. Aargh!
Best of luck to your dd.