K.K.
In some ways 2.5 year olds are still "babies"....why make them grow up too fast anyway? It is natural to "regress" when there are changes...even adults do that if you haven't noticed. :):) Why would there be harm in letting her have a binky? Comfort is comfort. Or she could use her thumb which is actual a very good way to self soothe. Either way, I wouldn't worry about this....just do what it takes to make her feel safe and secure and enjoy the fact that in some ways she is still a "baby". Before you know it she will be a teenager and you will miss these times.