Yes, these family collaborations are fraught with dangers, as you can imagine. There's nothing wrong with having a family member do the editing if the person is qualified and agreeable.
I have dealt with the same issue myself. Does one's participation require a separate byline? This is especially an issue in Amazon, where you can list multiple authors if you wish.
Without a doubt you should give a generous acknowledgement to your mom's assistance on the copyright page. If it's nonfiction, I would certain add her name to the credits on the Kindle details page.
Typically, if it's a fiction work, you should only have a single author even if someone helps substantially with the editing. It's rare that a fiction work has two authors.
With nonfiction, if it's a personal memoir, it's not uncommon to have more than one name (with the first name being the primary author). But having a second name has a social stigma because it implies that one of the two is a ghost writer.
If you are writing a nonfiction work (about current events, science, psychology), it is much more common to have multiple authors (And no one would look down on you or the work for that reason). For example, if you look at the Oreilly books (which are considered top quality in the IT field), typically you will have a technical expert be the lead author and then someone with a strong background in publishing be the second author. That combination works well. But the second author also does a substantial amount of writing/organizing of material.
It probably is a bit presumptuous for your mom to ask for 25% after the fact. If anything, this should be a lesson for you to clarify these royalty issues at the start so you don't encounter these disputes.
In general, you should err on the side of giving too much credit rather than the opposite. I think your mom wants acknowledgement that she made a valuable contribution to your efforts, and getting a share of the profits is one way to do this. But it's unfair for her to arbitrarily set a rate after the fact.
Here's how I would approach it. I would say, "Mom, clearly you helped a lot on the production of this book, and you deserve the credit. But we never talked about a royalty split, and it would be unfair just to decide you are entitled to "25%". I think that 10/15/20% would be more appropriate -- even though I admit it doesn't take into account your true contributions."
(To support your argument, you might be able to draw up some numbers to suggest that you have spent more hours on the project than she has).
Generally the big issue in book production is lack of professional editing. Often editors want payment in advance rather than a percent of the royalties. In a way, your mom is doing a huge favor by agreeing to be paid by future royalties rather than charging you an hourly rate.
Finally, look at the big picture. Maybe your mom wants more credit than she is entitled to, but I also think you want this collaboration to be something you are both happy with. Paying her 25% seems to be a small price to pay to show your gratitude for her help and ensuring smooth family relations in the future plus preserving the happy memory of working together.
(And if the books hits it big, then next time you can choose to do it alone or clarify the royalty arrangements so that both of you know what you are getting into).
By the way, here's some typical industry rates http://www.the-efa.org/res/rates.php and http://freelancewrite.about.com/od/finances/a/Freelance-Writing-Rates-List.htm
Not knowing what help she gave or how much time she devoted, I would say that 15-20% is a fair rate to give to a second author. But now is a time to be generous, not stingy.
Update: Both of you should have a candid conversation about who owns the copyright. All editors feel a sense of "ownership" about book projects, but that doesn't imply that the person deserves to own the copyright. I would urge against putting two people on the copyright line unless it's unavoidable. Having two people own the book copyright makes it legally complicated for you to sell or authorize rights of distribution. It's much more practical for one person to own the copyright. Personally, I feel that I have made substantial editorial contributions for a number of books, but I feel almost a ghoulish pride in my willingness to let the author take all the credit. Maybe that's just me though...