Good that you have wills and POA in place.
Spend some time to sort out her "paperwork" and "life admin", i.e. check you know what investments she's got (shares, pensions, insurances, etc), bank and savings accounts, etc. Usually for old people, there's lots of little things hanging about, so amalgamate and standardise to make it all simpler (both during her lifetime and following her death), i.e. sell odd small shareholdings (most seem to have a few hundred quid worth of BT, British Gas, Standard Life, etc). Many have several different relatively modest bank/savings accounts - just transfer them all into one. Check that she's "tax efficient", i.e. maxing out her annual ISA allowance by transferring in the max each year from other savings accounts so that she's not losing out by paying tax unnecessarily (plus hassle of dealing with HMRC to declare/pay). Check how household bills/utilities/credit cards are being paid - again, standardise using direct debits so you/her don't have to remember to pay bills and risk late payment charges. Check her bank statements to check everything unnecessary has been cancelled, i.e. old subscriptions, potentially duplicated TV packages. Do comparison websites for landline, mobile phone, broadband, TV, house insurance, car insurance, utilities, etc. If she's living on her own, check she's getting council tax relief for single occupancy. These are all the things she is probably not capable of doing herself. When someone had been doing things in the same way for decades, they lose the will/ability to check, shop around, etc. If her memory is starting to go, she'll still be capable of helping you/working with you, to sort out her "life admin". If you leave it too late, she'll lost interest, probably won't remember what investments/savings she has etc.
Yes, it sounds "money grabbing", but it's really not the intention. I've dealt with dozens of old people whilst alive and after they've died helping the executors and have seen how much time and effort it takes to, literally, sort through boxes and boxes of paperwork, not knowing whether a creased up old share certificate is still valid or has been sold a couple of decades ago, seeing taxes being paid in the past completely unnecessarily (income tax, council tax etc), seeing subscription direct debits for both Sky TV and Virgin TV! when there was only a Sky box, etc. You have to put your "practical" hat on, as well as your "emotional" hat.
The other big thing is a lifetime of "clutter", possessions, etc. Find time to go through old photo albums to bring back memories, talk about all their "bric a brac" as, again, it brings back memories, i.e. souvenirs bought on holiday or a "special" first gift from husband when they first started dating etc. Dual purpose - you learn more of her past/history/memories, and it's good for her to remember things she may have forgotten, maybe the last opportunity. You'll also know what was important to her and what wasn't - i.e. keep the ornament that they bought on their honeymoon, but donate all the ornaments bought by relatives for Xmas/Birthdays that meant little to them. Likewise with photo albums - you can't keep them all, so looking through them during her lifetime will tell you what was important for her, who people were you don't recognise (i.e. distant relatives at weddings etc), so you know what to "weed out" to keep, and what will ultimately be OK to bin.
Also check with her if there's anything she's lost, and help her find it, especially in a house full of a lifetime's possessions. One big regret of mine is my mother's wedding album. In her final few weeks, she kept looking for it, and had convinced herself (and upset herself) that it must have been thrown away accidentally. We had a cursory look around the house at obvious places, i.e. on top of wardrobe, in sideboard cupboards, etc., and I even went into the loft to see if it had been put up there. Sadly she died before finding it and I think it really upset her as she wanted to look at it one last time. Whilst clearing her house, we found it! Under her bed, wrapped in a duvet cover! She'd put it there for "safekeeping" but had forgotten she'd done it!
I'd finally say, don't delay. Sometimes dementia progresses VERY rapidly. My mother was forgetful for a few years, getting worse slowly, but still mostly functional, but then over a couple of months, she went from being able to go shopping herself, to not being able to recognise us! It's scary how quickly it can deteriorate so much.