Tire Pressure Question

Hi, can anyone help with this question? I have a friend that drives a 1999 Kia sportage. The Mfr. recommends only 26 lbs in the tires. This seems kind of low. At that pressure the car is like it is setting on balloons. You can push the front corner sideways and it jiggles like setting on a bowl of Jello. She is using GoodYears that have a max pressure of 35 lbs I think. I know the handling and gas millage would improve greatly if I out 34 lbs in them. But will it make the car unsafe causing less traction or maybe tip over easier? Also, will the tires ware faster? Just trying to help out a friend, Thanks