Ridesharing these days is a euphemism for Uber and Lyft, but there may have been a credit for car pools back then.  Maybe it only applied to employers but the instructions were not clear.   In any case, she might not have signed the joint return but not filing her own is evidence that she ratified it.  Of course we all know that rules are suspended for people getting a divorce, because they are the only ones it has ever happened to.