I'm sure others with more direct experience will be here soon enough, but I hope you have asked her the usual professional questions. If she's legitimate, she will have no difficulty or reluctance in answering them.
What publishing houses has she edited for, during what time span(s)?
What published books did she edit?
How long has she been editing independent of any publishing house?
What books has she edited since she began working independently? Who published them?
Does she offer a sample edit on a short bit of your writing--say chapter one--at little or no cost to you?
Will she make available the email address or phone numbers of those for whom she has edited in the last two or three years so you may contact them about their experiences?
Maryn, who knows there are editors, and then there are editors