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.