Question for our cat owners!

[MiRaja]

Take her to the vet immediately.  Peeing outside the box is not generally a behavior issue unless the cat has been declawed.

It is much more likely a UTI or a bladder infection, as has been said already.  When the cat goes pee in the box, it can hurt more, because the litter burns, as well as it burns coming out.  I've had a UTI, they're very painful!  So, your cat is associating the litter box with PAIN, and so goes elsewhere in attempt to find somewhere where it doesn't hurt. 

On the subject of litter boxes, you should almost always have one litter box for each cat plus one.  If you have one cat, you should have two boxes.  Three cats, four boxes.  I have lucked out in that my cats all get along very well, and I have a jumbo litterbox that they all use without issue.  I do live in an apartment, however, and when I buy a house, which will likely be multi-story, there will definitely be more litterboxes. 

Just think about this:  You're upstairs, would you want to use a bathroom all the way in the basement?  No.  So why do you think your cat does? 

Yes, female cats can spray, especially unfixed, which is why it is *always* important to fix a cat before it reaches a year old, because the behavior will not always dissipate after the cat has begun the behavior and has been fixed AFTER the fact.

I can say with experience that I have *never* had a female or a male cat spray in my home, and it's because I've always followed that tidbit.  I used to work with some of the shelters, and there were times I had 12 cats living in one space.  I never had an issue.  Ever.  This doesn't sound like the OP's cat is spraying, rather is sounds like she is trying to go to the bathroom, which suggests a biological issue. 

And yes, UTI's can show up fast.  It can be a matter of the cat not getting enough hydration, just like in humans, though cat UTI's can be caused by an additional bunch of reasons including stress, but a lot can be prevented, too, with just bathroom and water needs.  The best way to prevent UTI's is keeping the litter very clean, scooping it often, and also access to clean, fresh water.  Something my roommate and I have been butting heads on, because getting her in the habit of changing the litter and water bowl has been like pulling teeth.  I scoop every other day, or try to, and I try to change water at least twice a day.  Again, you have to think about what you like.  Do you like stale water that has been sitting for twelve or more hours?  No, and neither does your cat.  Do you like using a dirty bathroom?  No, and neither does your cat.  It's a great rule of thumb and a commonsense solution for a lot of pet ownership.