She has that in Tyrion already. He knows Jon is honorable from his time spent with Jon at The Wall.breh, no one is talking about ships. no one cares about KL and the throne (well I don't...), i'm talking about end game. dany and jon will have to unite (IMO), the first step in that is having someone who knows both sides and can keep them from seeing each other a threat, they need to unite to help defeat the WW's.
Theon and Jon weren't close. Theon was Robb's homie and didn't like Jon Snow at all. Plus after what Theon did at Winterfell, Jon isn't going to be all that interested in having Theon vouch for him.