Paper contributions and first authorship
Authorship questions are among the most difficult aspects of academia and where feelings may run high. First, it seems you have a reasonably good working relationship with your advisor, it is good that she asked you. Some would tell you, some would just do it. So from this perspective, your advisor does what she (in this case) should.

The question of ordering of names is tricky and there are no simple rules, or actually there are simple rules, but they may be difficult to apply in the individual case due to a variety of reasons, including anything from personality clashes to just simple difficulties to asses who has done most. There are examples of point systems where authors are given points depending on what they have done and how much. In one case, the study design and writing (discussion) had much higher weight than aspects of experimentation and data analysis. the problem is that one should agree on such matters before starting on the writing.

So, to assess your and your co-author's contributions, you need to split the project down in at least four parts:


Who came up with the original idea and designed the study (high credit)
Who did the experimental work (equivalent) that generated the data
Who did the analysis (equivalent) of the data
Who contributed to interpretation and discussion towards the conclusions


Each of these have some weight with 1 and 4 most often larger than 2 and 3. Then when several persons split a chore you need to figure out roughly how much of each point each person has contributed. This would then give you a profile of who has done the most (important) work etc. I completely agree with anyone who would say this is easier said then done but you probably see the principle.

So to the question(s). If you have work earlier or later on this is of less significance, it is what type of work you have done and of course how much. figures can be extremely important. Good graphics convey the message in condensed form. plotting data is, however, in most cases not much more than a technical issue. Creating conceptualizations of processes, events etc. can be key to the paper so making figures can be a considerable input to be counted.

You can also check the text on this link for a text on authorship. An example of how authorship can be determined is given on AuthorOrder