My 11 Yr Old Female Chihuahua/schipperke Mix (14-15 Lbs) Has

My 11 yr old female Chihuahua/schipperke mix (14-15 lbs) has been favoring her back left leg. I thought it was her knee, but when I (gently) lifted the leg out to the side to see if she reacted as the hip moved, she winced. She has had knee problems in the past (dislocating) but it hasn't been an issue in over a 6+ years. When the knee would dislocate she would come to me to 'put it back.' This is totally different, she is not moving around much at all and I think she has more pain.