You cannot make an EPA or Enduring Power of Attorney anymore, they were replaced by the LPA or Lasting Power of Attorney in 2007. If she has capacity to understand in the moment what an LPA is and does, she can sign it. If she has lost this capacity, you will have to go down the deputyship route.
Costs for an LPA are £110 for registration with the OPG. There is a financial and a health one, so that would double the cost, but it's worth doing both. You can get 50% off if the donor has an income of under £12,000 a year, and it's free if the donor is on qualifying benefits.
Deputyship is more expensive, it costs about £400 to start with and I think there are yearly admin costs. All these costs can be reimbursed from the donor's money.
And yes, it's perfectly possible to fill in those documents yourself and save yourself any solicitor costs. The forms aren't too difficult, come with a lot of guidance notes and can be filled in online.
"Lasting Power of Attorney (LPA) replaced Enduring Power of Attorney (EPA) on 1st October 2007. EPAs signed prior to that date are still valid and can be registered but the LPA is far more flexible and you have the option of taking out either a Property and Financial Affairs LPA or a Health and Welfare LPA, or both."
Link to the site below for the whole story.
Second link is to the ".gov.uk" site where you can do it.
Hope it's of some use, I think all you need to know is there laws may differ if you're in England, Scotland or Wales.
Feedback to OPG was that people were put off making LPAs because of the complexity of the process and the need for 2 certificate providers if you didn't use a solicitor. I am pleased to report that the LPA process, and the forms, have been simplified this year and there is now an online service for completing the forms. https://www.gov.uk/power-of-attorney/make-lasting-power
The guidance online is in plain English and is straightforward. I wasn't sure if the certificate provider could be someone who doesn't live in England or Wales. I rang the helpline and was told that the person I chose could live anywhere, it was only my residence that was relevant.
I am in the process of completing my 2 LPAs, for Finance and for Health and Welfare. My income is currently zero but will be over £12K from January 2016 when I start to get my employment pension, so it seemed like a good thing to get on with it while it is half price. I filled in the forms online, paid my fee, and printed them off. Now that I have paid I am motivated to complete the registration process.
I have signed as the donor, with a friend being my witness and certificate provider. Now I need to get all my attorneys (OH and our children) to sign and date their pages with a suitable witness for each. Once that's done I will post the forms off to be registered.