Stutter could be so different

I went a local NSA meeting last night. There were 8 PWS attending. One lady from  a nearby city which is about 40 miles away joined the meeting. She spoke quite well for general conversations. I could not feel she ever stuttered when she was giving the five minutes introduction. However, when she was asked for reading a paragraph. She spent about 5 minutes to read about 100 words. She stuttered almost every words. This When she was asked that if she stuttered when she was reading alone. She told us in that situation, she stuttered much less.
It is so surprising to me because I did not stutter at all when I am reading. There are many PWS can read quite well while could not talk. If I examine the feelings of reading and talking to another people, the tension is quite different. I feel tension when I speak to other body, however, she feel more tension when she is reading.
To be relaxed, confident, firm, assertive are the keys for improving my speech.