Credit with helping to write a PhD thesis
In some fields, almost all work is done as a collaboration. In these fields, it is not at all unusual for this collaborative work to end up in a student's thesis. However, the thesis text should clearly state "This chapter describes joint work with X" (e.g. in a footnote).  

However, to really get credit for this joint research, you should prepare a manuscript and try to get it published, or at least release a preprint you can put online (if there isn't time to get it published before you apply to grad school).

For the editing assistance, the most you can get is a thanks in the acknowledgements, and help with editing is not likely to impress an admissions committee.