The great differences between the Christianity of the Taiping and the West will make relations difficult to say the least...
I mean, Hong Xiuquan claiming to be God's son (and somewhat sidelining/usurping Jesus' role); then you had West King Xiao Chaogui claims of being a vessel/speaking for Jesus Christ and East King Yang Xiuqing taking up the mantle of the Holy Ghost; and the harsh treatment of Nanjing Catholics; all of this'll be hard to swallow for westerners.
Taiping claims to universal rule and just generally acting superior- refusing diplomats access to Hong himself and such- would also be grating for Europeans (similar issues had frustrated their early dealings with the Qing).
After being repulsed at Shanghai, and the westerners started openly supporting the Qing there was also a more traditionalist, anti-western strand of the Taiping. In any case, the clashes at Shanghai and European officers in the Ever Victorious Army (if these occur ITTL) would leave the Taiping with distrust/resentment of the west.
Maybe if you kill off Hong Xiuquan and give a regency to his cousin Hong Rengan, who spent six years in Hong Kong, then he can make the movement more moderate and acceptable to Westerners?