Having cared for a little boy for 2 years who displayed multiple signs of an LD, I researched many things and spoke to lots of professionals on how to handle his parents. They directed me towards an observation sheet for developmental milestones. It is a district developmental screening test developed in Nippissing but used across many regions including Halton that I know for sure. I actually got the info from Halton Resource Centre. It is a yes or no sheet. You do not give your opinion on anything you are just making an observation over a period of time. The tests are all based around the typical age when your child goes for a Dr's check up and also more frequently when they are younger. The screen tests state that if any are answered no, then a visit to the family doctor to discuss this specific milestone is advisable. I do this for all children and parents are super happy to have such specific developmetal information given to them to take along to their childrens dr's appointments. This way I am not singling any one child out, and most Dr's appreciate this as if you spend more time with the child than the parent then they may not be in a position to observe certain things.
As far as a quick fix for the fingers in mouth, why not buy an ark grabber. Just a few dollars and are supposed to be very helpful. The fingers in mouth is more than likely the cause of the drooling and the lack of speach. her tongue and jaw are busy chewing instead of developing her oral skills.
for the ark grabber http://shoponline.pfot.com/otmomfaves1.html
for the developmental screening tool www.ndds.ca
Hope this helps but otherwise the best advice I can give you is document everything as you see it NO OPINIONS and make sure you take time for yourself. It can be very taxing dealing with a child with special needs regardless where on the spectrum they fall and especially as you are likely giving this more attention than her busy mother.
Send me a private message if you need any additional info.