All the above is excellent advice.... but I would add that when she whines to you, talk back in a soft soothing way. Cats usually vocalize to their colony when they enter a space and to let their peers know their location. This feral is including you in her world, include her back. Sitting close without eye contact and playing with something that you then leave near her would be a help too. (This could be a treat or a fun toy). For cats to touch involves trust. You might try petting your other cat while the feral is grooming him. Group grooming is a great way to break the ice.

good luck. it takes time but some of the best friends I ever had once hid under the bushes.....