Female cat spraying??

Have any of you guys experienced a female cat spraying out of frustration?

I mean, a cat that sees some cats outside, and sprays the windows. This cat is spayed, but the owner feels it might have been done incorrectly (though she hasn't told me why), and now has this problem occurring.

Anyone have any ideas as to what causes this, and possibly how to handle it? I've never had a cat, myself, that did this, so I'm stumped.

Thanks!

Edit: Thought I'd post her exact question and situation, so you guys could read:

I have a 4 yr. old female calico cat that was the offspring of an alley cat. She may have been taken from her mother too soon (5 wks?). She seemed to be very well adjusted and happy to live with me until I had her spayed. I think the vet did a miserable job of it and didn't give her enough pain med. I'm not sure.
Anyway, the first year of her life with me she was on the 4th floor of an apartment building and I wasn't supposed to have a pet, so she was not allowed to go outside at all. It didn't seem to bother her. She has always been left alone too much, because I am single, working, and was first looking for a house, now trying to make enough money to pay for the house. But since we have lived in a home of our own she has been allowed to go outside.
There are several other cats that come around while she is inside and they get her agitated, and she will run from one window to another, and she sprays by some of the windows. When I'm home, sometimes I can get her to go outside, but when I'm at work she seems to let out her frustrations this way. I have never known a female cat to spray like this before, and I really don't know how to break her of this habit.
I'm still working on regaining her trust and affection since her spaying, so I don't like to punish her harshly. Do you have any suggestions?

First of all, I thought my vet botched Ophelia's spay, too!

a)take the cat to the vet & get a urinalysis to rule out any infection or crystals

b)the cat may have to confined indoors to see if that helps the problem(You never know, some cats are different)

c)buy a feliway diffuser & plug it in. I was skeptical until I bought one & it really works!

d)cover the windows so she can't see the other cats

e)get a good enzymatic urine cleaner & remove all urine stains. use a blacklight to see them. I use Nature's Miracle.

Yes females do spray, just not as commonly as males.

I agree with above post to check if your cat has a UTI or crystals.

Very cool. Thanks, guys!