It's really hard to tell with the handwriting because Marion's changes so frequently, even in terms of characteristics. However, there are some striking similarities across the handwriting samples that make me think that it was Marion who filled out both passenger cards. I'm not an expert but it's an area that I'm really interested in, and a lot of the time it's not how visually similar the letters are but how they are formed, as people have natural habits that they probably aren't even aware of.
One characteristic that sticks out to me is the way that Marion in multiple samples writes her capital 'E'. If you look, you can see that she forms what I am nicknaming a 'fragmented E', where the letter looks as though it is collapsing/exploding - the dashes that form the 'E' don't touch the original strike of the letter and they sort of collapse into each other at an angle. In my opinion, this is consistent throughout the samples.
There are other letters, too, with which this is the case but this is probably the most noticeable.