S.F.
I had a preemie as well (32 weeks too). I tried a gazillion different ones. The only ones she would take were the Enfamil ones I got at the hospital. I found them at the enfamil website and ordered them that way. I washed and reused, but keep an eye on them, they are NOT for long term use. Here's the link..
https://www.enfamil.com/app/iwp/consumer/productCategory.do
You just have to select Nipples as the acceessory in the drop down box... HTH.
I assume you can order the Similac ones too if that is what she is stuck on.