I think your biggest problem is thinking that anyone is claiming that Lucy was 100% bipedal.
The definition of a transitional is one where the morphological features of a creature are shared between its parent and daughter species.
Lucy could probably both walk upright and climb trees well. Scientists would be pretty outrageous if they claimed that in one step, aboreal apes decided to stand up and walk out of the jungle. It is more likely that there was an aboreal ape that simply was also pretty good at walking which allowed to to exploit new resources that pure aboreal apes could not.
Even if you look at modern humans. We are still very good at climbing trees. I remember seeing a tree climbing race between a chimp and a Samoan. The chimp won but not by much at all.
The last important point to mention is that even if it could be proven that Lucy truly was non-bipedal, it does not change the vast amount of other morphological evidence that show Lucy as being divergent from other great Apes and more like humans. Lucy's hips are a great example.
Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)