It does depend how big the advances were though, and how many copies have sold already. Her first book deal with Penguin in 2013 was for £25,000 according to her Wikipedia page (which may be incorrect, that's large and I think probably split over two books). So let's hypothesise she was paid an advance of £10,000 for the first one, which would then have been split down into something like £2,500 paid on signing the contract, £2,500 on delivery of the manuscript, £2,500 on acceptance of the manuscript (i.e. after editing) and £2,500 on publication.
Before she got any further money from that book in royalties, she would have to 'earn back' the advance - in other words, the first £10,000 in royalties from that book will go back to the publisher, and if they offer it at a deep discount to kickstart sales, the royalty will be discounted too. Once the advance has been paid back to the publisher, royalties get paid twice a year, so it's not exactly a constant cash flow.