Your cat shouldn't be able to jump a gate at the stairs since the angle of the stairs gives the cat a significant disadvantage. Plus, when you're hungry or have to use the bathroom, do you feel like leaping? Putting a gate a few inches off the floor will only leave you open to the risk of a baby arm or leg getting caught underneath when exploring or trying to get a toy that she dropped down the steps.
I have a gate that is extra tall with a pet door in it and it's wonderful. You can find it online at improvements.com
http://www.improvementscatalog.com/home/improvements/7929...
We also have one 6" extender piece.
We used this gate for my son and my husband just put it up again for our 11 month old daughter who's very quick on the belly crawl across the hard wood floors. It's a little spendy but well worth it.