Raven had really never seen actual telekinesis before. She had watched Magneto direct nukes in midair, and Emma had a fondness for making illusions to get out of actually doing things, but real, actual telekinesis? Never once.
So she immediately agreed to the chair ("Sure, that would be nice.") in the hope that Wanda picked it up and floated it over instead of just reaching. It was sick how desperate she was for some kind of new connection, especially with another woman; Erik, Charles and Hank are good, but she missed having Angel around, even missed Emma's obvious attitude problem and her weird elitism.
(Technically speaking, Mystique could walk if she wanted to, albeit with a bad limp and aggravating the damage. Not worth it.)