House cat sleep, eat and play. 85% is about average. I wouldn't be concerned unless she shows signs of lethary even when not sleeping.
I wouldn't worry about that like everyone else said cats sleep more than they are awake. We always used to joke when I was a kid that that cats get tired from taking a nap.
Some cats are more docile and layed back, or is it laid-back, than others. My 2 younger female cats turned 1 on May 6th. If they are outside....they are more active. In the house... they seem more likely to lay around, or is it lie around? Maybe they are bored or more relaxed, either case I think it's normal . If they are not having any "sick" symptoms they are, in all likelihood, just fine. I've found that when they get older they sleep even more.
It is my understand (and experience) that on average cats sleep about 13-16 hrs. per day. We have 2 cats that are "night prowlers" and spend most all day sleeping soundly. Hope that helps.