I thought Ruby didn't use her hammock either until I told someone that there were poos in it. They told me if they're hanging out in them long enough to poop, they like them!
sounds like she's enjoying using her hammock as a litter box, lol. does she have a litter box? if not, give her one and wash, then move the hammock up higher. that's my suggestion.
She's probably not letting you see her in it cause she's not comfortable yet. I was frustrated too, but later my chinny got used to the hammock and would nap in it all the time. Try not to stress about it too much, she probably senses that you have tension about the hammock