Advice for dealing with a pushy Christian friend....?

I have this old hs friend that is being awfully pushy with her Christian ideals toward my younger sister. I haven't been on my FB in a while so while checking things out, I decided to skip over to my sisters page and check her out- say hey- whatever. She used to be very active on her FB but now nothing for like 2 months. Literally like every 4 days or so, my old hs friend is leaving her Bible quotes. There are comments from her saying that she is praying for my sister, and that she hopes that she will get her act together soon and find the Lord. (and btw she's not a bad kid) There is nothing but these types of comments on my sisters page anymore. I think she's abandoned it to get away from it all. Now don't get me wrong here, I'm not bashing Christians or anything. I just don't see why an adult woman needs to badger a teenager repeatedly with Bible quotes.

Does anyone know of an appropriate way for me to address this with her? Let her know that I don't really appreciate her smothering my sister in this manner? Any advice about how to maturely address this situation will be appreciated.