Board Thread:Skyrim/@comment-10207438-20130919024334/@comment-82.2.29.143-20140106055536

Balgruuf was of a mind to remain neutral, Tullius was of a mind to let him and Ulfric was of a mind to attack if he did. If this situation was not influenced in any way by the dragonborn, and for the sake of arguement Rikke failed to convince Tullius to change his mind, Whiterun would have faced the Stormcloaks without the legion to help bolster their defences. I believe in this situation Lydia would fight the Stormcloaks since as far as she would be concerned, they would be attacking her home without reason.

If Rikke succeeded to change Tullius' mind, Lydia would join the legion forces to defend her home.

Imo it is only with the influence of the dragonborn that she would aid the Stormcloaks. I can't really see any reason for her to do so otherwise.