I was thinking that - maybe just to offer to meet with her mom. 'This mom even said it may not be my daughter's issue - my daughter seems fine about it -- and the thing is I usually know what is going on if there is a so-called big issue - as big sis steps in. Often times overstepping her boundaries in support of her sister so I always hear about it.
I did know of this issue as we talked about it before -- I just said everyone is different and sometimes some kids just don't want to be as social and want just to stay in rather than meet up. Just respect her wishes and get together when you can.
I honestly think in this case it is less a texting issue rather than different personalities. My daughter likes to get together with her friends -- this girl being one - and this girl seems to like more alone time. It just comes through texting because that is how they communicate. I don't think it would be much different if they talked on the phone.
My daughter did compromise and told her she wouldn't get angry at her any more for not wanting to get together.