Hmmm... does she do the same thing when she is not in the stroller? She may be feeling insecure and might have the idea that by keeping her in a stroller that you also don't think she's safe out in the world. Just guessing here...
Why don't you try walking her on a leash and ask other people to give her a treat? Maybe then she will trust others as they will be the source of good things - oh and make sure the treat is a REALLY good one.