Quoting La Reggaetonista:" I don't not want her to have it. Technically she is still a baby, to me anyways. And I don't want to ... [snip!] ... to take it away. My grandma said there are bigger worries than a binky. I'd rather fix her teeth later than upset her now..."
Then you let her have it!
Seriously, you can do a quick google search to find tons of info to back up the fact that kids with autism sometimes need oral stimulation, self regulating items, etc. If they want to make it difficult for you, you can hit them back with the proof that she needs it for her comfort right now.
You are the mom, you know her. Period. Don't let them bully you. You need to have your sanity to so you can get through the day, and if a soother gives you that, then so be it. If she has autism, you have bigger fish to fry than her sucking on it at bedtime.