Is she sinning if she turns on the television for someone else?

The television is something that may be used for good or evil. You may watch beneficial Islamic channels or permissible programs, or you may watch movies and soap operas which include evils and sins, such as nakedness, mixing, crime and corruption. Whatever is good or permissible, it is permissible to help a person watch it by giving him the remote control or turning on the television. Whatever is false and evil, it is not permissible to help with, because Allaah says (interpretation of the meaning):

“Help you one another in Al‑Birr and At‑Taqwa (virtue, righteousness and piety); but do not help one another in sin and transgression. And fear Allaah. Verily, Allaah is Severe in punishment”

[al-Maa’idah 5:2]

Rather it is essential to denounce that as much as one can, because the Prophet (blessings and peace of Allaah be upon him) said: “Whoever among you sees an evil action, then let him change it with his hand [by taking action]; if he cannot, then with his tongue [by speaking out]; and if he cannot, then with his heart – and that is the weakest of faith.”

Narrated by Muslim (49). 

See also the answer to question number 3633. 

And Allaah knows best.