Cat urinating on furniture

Question
I have a year-old, female, indoor cat.  She has lived indoors since she was born a stray in my garage.  She has always used a litter box and since she first learned to use it I have NEVER known her to go anywhere else.  However, she has started urinating on a chair in the house, and also she went on a blanket that was on the floor.

Why in the world would she start doing this all of a sudden.  This began about 2 weeks ago, which is also about when she went into heat for the first time.  I have an appt. to spay her next week, but could that be the reason for her sudden behavior?  Also, she has been eating some food for the past month which is specially for urinary tract health since we had it for our other cat. I have since changed her back to the regular adult food she liked, but could the other food be a factor?

Please help, I'm desperate to curb this frustrating behavior!

Thank you,
Brittany

Answer
She is most likely marking her territory due to her heat cycle.  Spaying her should resolve the problem, however, I would also recommend having a urine sample checked to rule out urinary tract infection.

Feliway can help reduce urine marking and Cat Attract Litter is also something to consider using to get her back to the box.