my chi slips out of her harness

Question
hi there. my chihuahua is on hyper alert mode when we go for a walk and if something scares her, she can slip out of her harness by backing up and run right home. do you have any suggestions on the type of collar or harness that would work best on my girl? she weighs about 11 pounds, and she has a large neck, so a collar is hard to find too, because there isn't much difference between her neck and head size. i am making her sound terrible looking, which isn't true.she was a rescue dog and i do not know what her parents looked like, but they probably were not tiny dogs themselves. her heart is as big as she is and she is definitely the love of my life and i really want to find a solution to be able to take her on walks without the danger of her getting scared and running home. thanks for your help!

Answer
If you tighten the harness just to where it doesn't hurt, but is still rather tight, this is usually prevented. However, if she starts to pull on the leash, pick her up and carry her home to avoid her being choked. Let me know if this works, or if you have already tried this, send me a follow up, and I will give you a different answer.

Ashten