pee in sink
There are several potential reasons. As you said yourself, she may be going into heat. Female cats often spray or urine-mark when they are in heat. Maybe she is trying to get you to post a personal ad in the paper for a handsome tomcat!
Another reason could be that she may have a urinary tract infection, although this would be unusual in such a young cat.
A third possibility is a litterbox problem; for instance, she might just like the cold smooth surface. Sometimes an extra litterbox with *nothing* in it will satisfy this particular preference. Or, the box might not be to her liking for another reason--cleanliness is a biggie. Lots of box-related issues can come up, especially when there are multiple cats. (See several articles on the subject at
http://www.littlebigcat.com/index.php?action=library)
This is not typically attention-seeking behavior in the sense of wanting more petting or food; but inappropriate urination *is* often a cry for help, a telegram to you that something is wrong.
Cats always have a reason for everything they do, and in feline terms, urine is a means of communication. She can't call you on the phone or write you a letter! So please try not to get annoyed (think of all the *worse* places she could have gone!), but make the effort to understand why she may be doing it.
Hopefully having her spayed will make the problem just go away! Under the circumstances, going into heat seems the most likely explanation.
Cheers,
Dr. Jean