Baby sucks on her sleep sack...help!

So my 20 week old daughter loves to chew/suck on her bib or burpcloth during the day. But now this has turned into her sucking on her sleep sack at night. She will literally grab down and get some fabric and put it in her mouth and she gets it soaked form all the drool and saliva...but this is how she puts herself to sleep. I've tried giving her a pacifier but she spits it out and goes back to the sleep sack....any suggestions?!?!