The majority of my students (first year undergrad) are lovely and attentive and I don't think this girl is particularly unpleasant in her own right..... but I can't see how you could not think for a moment that it is very rude to sit very blatantly texting through most of a seminar.
The problem is that it's difficult when you're not actually a school teacher, and they're not actually a child, to pull them up on bad manners like this without seeming schoolmarmish.
Would you expect this? Would you do it - if you were really really bored, which obviously I hope she is not and worry about?
Quite a few of them do it from time to time - but she does it LOADS and it's starting to really infuriate me. Do you think she would be surprised/appalled to be pulled up on it? And would I be unreasonable to collar her and tell her to bloody stop it?