What can I do about my cat?

I have a VERY small 17-week-old kitten, which I am trying to introduce to outdoors. I took it very slowly and today I tried to take her for a walk in her harness. She was petrified. She hates being outdoors at all. She has gone into the garden before but she will only go out if she is accompanied by a person or our older cat. The other cat we have is a very large, very powerful three-year-old male. (The cats get on very well together.) He tries to encourage her to go out, but she won't. The younger cat (the one who hates being outside) was taken from her mother a few days after weaning.