And then in this episode, when she gets telepathically linked to Clara, she’s corporeal within the mind conference, and then Clara is telepathically linked to Sexy, so that allows Sexy to finally transmit River in a corporeal form, hence The Doctor being able to grab her arm and kiss her. (But, Sexy refused to make this intimate moment viewable to Strax, Jenny, and Vastra.)
"Doctor Who: You’re always here to me. I always listen. And I can always hear you.
River Song: Then why didn’t you speak to me?
Doctor Who: It would have hurt too much.
River Song: I could have coped.
Doctor Who: No, it would have hurt me."