That is basically correct.  An ovio-hysterectomy removes both the uterus and
ovaries, and she will no longer have anything to tell her body to produce
female hormones.  The only difference between her and a boy cat will be the
appearance of their 'nether' regions, and the way they pee ;)

In some circles, spaying/neutering of animals *is* acutally called
"desexing".

At any rate, it will ultimately be better for her to be spayed, for many
reasons.  The following is copied and pasted from an Australian cat-lover's
email:
-----
Desexing

It's amazing how many people profess to love their pets, yet
do not bother to have them desexed. There are many benefits
to desexing as you will see in the links below.
Following is a reproduction chart. Allowing two cats and their
offspring to breed for 10 years will produce 80,399,780 cats!
(Statistics from American Humane Association which assumes
two litters per year and 2.8 surviving kittens per litter)

1st year: 12
2nd year: 66
3rd year: 382
4th year: 2,201
5th: year: 12,680
6th year: 73,041
7th year: 420,715
8th year: 2,423,316
9th year: 13,968,290
10th year: 80,399,780

Each year tens of thousands of abandoned cats and dogs
are euthanized because homes cannot be found for them.
Please do your part, desex your pets.

Useful links:
In Hope, An Animal Shelter Story
http://www.brightlion.com/InHope/InHope_en.aspx
Health Benefits of Spayed & Neutered Pets - Pawprints & Purrs
http://www.brightlion.com/InHope/InHope_en.aspx
Neutering your cat - FAB
http://www.fabcats.org/neutering.html
Early Spay/Neuter in the cat - Winn Feline Foundation
http://www.winnfelinehealth.org/reports/early-neuter.html
Early Spay/Neuter in the Cat - CFAINC
http://www.cfainc.org/health/early-spay-neuter.html
Benefits of Spaying or Neutering your Cat - CatsInternational.Org
http://www.catsinternational.org/articles/feline_care/benefits_spaying_neutering.html
Spaying & Neutering - PetEducation.Com
http://www.peteducation.com/category_summary.cfm?cls=1&cat=1364
Early Spay & Neuter: The Benefits - Cats.About.Com
http://cats.about.com/cs/spayneuter/a/earlyneuter.htm
Neutering the Male Cat - MyPetsPages.Com
http://www.mypetspages.com/petinfo/feline/neutering%20the%20male.php
Neutering - MyPetsPages.Com
http://www.mypetspages.com/petinfo/feline/neutering.php
"Reality" A Testimony - Chris Benton
http://www.all-creatures.org/aip/nl-30apr2001-sam.html
Low-Cost Spay & Neuter Clinics
http://www.flippyscatpage.com/lowcostdesexing.html
National Desexing Network: Australia
http://www.ndn.org.au/

Please pass this information to all your friends, coworkers, and family who
have pets:
http://www.flippyscatpage.com/desexing.html

Flippy in Melbourne, Australia.
Email: <deleted>
Catpage: http://www.flippyscatpage.com

Please consider helping to keep the catpage online. Check these items:
Cat Stuff: http://members.westnet.com.au/flippy/kittystuff/,
Books: http://members.westnet.com.au/flippy/books/, and
Other Items: http://members.westnet.com.au/flippy/otheritems/,
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Since the default mamalian body plan is the female one, there isn't
all that much difference in looks between a queen and a female spayed
young - there is a big difference between a mature tom and a male
neutered young.

If you *really* want the true queen look, you can delay spaying until
she is fully mature - say at least a year old.  A couple of things are
almost certain:
1) you won't try it a second time - frustrated queens are destructive
and all-round intolerable
2) she will probably get out and get pregnant anyway.