Removing an author from a future publication
Most authorship questions are a gray area: she did contribute to the paper, but was it a significant intellectual contribution (which is one usual criterion), with emphasis of both significant and intellectual (or scientific)? That's for you and her to decide, taking into account the customs of your field.
From her point of view, I can see two reasons why she might be consider a rightful co-author of the paper:
- If the data collection was itself part of the scientific research, i.e. if it could not have been done by an unskilled worker following instructions. If so, then her data collection was significant (and it doesn't really ).
- If the conclusions drawn from the preliminary analysis were useful in tuning your final analysis, i.e. if her work helped design a better analysis method.
Though by your description it seems like she may not pass the threshold, it is true that having her as a co-author on an earlier publication (conference abstract) gives her a stronger case than otherwise. If her contribution was deemed important enough for authorship at first, and you now publish work that includes this contribution, why shouldn't she be an author? I don't think that authorship “dilutes” because other larger contributions were added…
In conclusion: you maybe have good reasons not to make her a co-author, but if she feels like fighting it, she does have valid enough arguments that it could get messy. I'd advise discussing it openly with her, but being ready to have her as co-author if she feels strongly about it.
I generally agree with the answer by F'x, but there is an additional point: You wrote in your question that
she is out of the field and I cannot contact her easily
I think that you shouldn't put her on the list of authors without her approval, for which you obviously need to contact her. Many journals that I know have the explicit policy that all authors need to approve the final manuscript.
If you don't have any affordable means to reach her, one way out could be to cite the conference abstract / poster where she is a coauthor, even if it is not a formal research publication. Thus, you make clear that her contribution was only to the results presented earlier. In addition, you could explain the particular contribution in the acknowledgments.