My experience was that utilites weren't necessariy easier. In general if you got someone in the UK not only would you get a lot of sympathy, but you were also likely to hear how their aunt had dementia.....
Overseas call centres were very different, going by the book and demanding POA etc. Honestly it was much easier to pretend to be my mum.
One thing I did was to type up a series of letters for her to sign to banks, pension companies and utility companies changing the address so things could come to me, and where possible giving me permission to speak to the supplier. Banks can give you third party mandate forms that your parents need to sign, which give you access to the account (and internet banking) without a POA being in place.
Pensions are important. My mums widows pension regularly sends out a form requiring her to get someone to sign that they have seen her and, effectively that she is still alive. If this went to her nothing would happen and the pension would cease.
I really advice that your Dsis goes to Rymans and buys a big level arch folder, a hole punch and lots of file dividers, then collects all the paperwork she can find and file by: tax; pensions; banks; utilities; things like funeral plans, National Trust memberships, ClubCards etc; wills; insurance; premium bonds etc. then go through ensuring you (probably but not so bad as it can be done from home) have access to each and every.
One thing I have been doing slowly is to move my mothers money to from longer term to easy access accounts. If need be get your parents to sign things like ISA transfer forms and have everything in an ISA account connected with her main bank account.
Also check if any tax returns are needed. I made contact with HMRC before their computer noticed that things were awry. There was still a formal investigation but we avoided some of the punative fines that could have been levied.
She should bring over her lap top and buy a PAYG dongle.
Whilst she is over think about making appointments with four local estate agents to come at half hourly intervals to value the house, tell you what works might be done to realise maximum value, and whether rental is a possibility in the short term. (Great for me as it gave me breathing space, allowed my mum to believe she could return home "when she was better" and gave me a deadline for house clearance.) This will give you a much better idea of what the market is like, and enable you and your Dsis to start making plans.
Once you have the numbers do a quick calculation to see whether you might be in inheritance tax territory, though like mansion tax I assume this is mainly a southern issue. Bills need to be settled within two months so this needs to be planned for. Its also useful to know how much money is available for private care.
Awful, I know, but also a chance to speak to funeral directors or the vicar (who in turn shoud be able to recommend funeral directors), gather together a list of people to be informed, venues for any funeral reception (sadly it will probably be the last time you see many from the extended family so worth doing well) and also make sure you know who the executor is. If it is a lawyer the more you do now the less they will charge. It all needs doing at some point. Plus my dads executor failed to do simple things like close bank accounts.
That and visit care homes...
Lots, but at least it will give your Dsis a sense of how much there is beyond the hospital visiting and care.