If I understand correctly, what you want to do is tell a single story from two different points of view: past and present. Two common methods for doing this in the novels I have read are what I will call flashbacks and parallel stories.
Flashbacks
I read several chapters in "Like Water for Chocolate" at the link in your comment under the question. That story appears to be structured thus:
- vehicle of flashback: Nancha's and Tita's memories of earlier times
- anchor to the present: preparation for the wedding of Tita's sister and Pedro
- plot to hold reader interest and guide story: Pedro's and Tita's intense love for each other
We want to find out whatever is going on and how this illicit love--or the ill-fated marriage--will end.
To use the flashbacks method, you will want to find similar aspects of your story to carry the plot forward, organize content, and hold reader interest.
Parallel Stories
I think you want two stories running parallel to each other, telling the same story from two different points of view. I don't have a sample story to link to, but I will try to describe as best I can, which means this section will be much longer than the section on Flashbacks.
I can visualize the Narrator of your story as an elderly woman sitting in a rocking chair on the back porch sharing her life story with a neighbour, friend, or relative. During this reminiscing they may be drinking tea and watching the birds and butterflies in nearby bushes. I can visualize this life story or reminisce interspersed with the events that are happening in real-time third person point of view, e.g. little Ranjo and her big brother. However, these events will be set in a different time period to tell the woman's story as it happened many years ago. That is what I understand you want to do, more or less.
The plot of your story will most likely be to show how the old woman became who she is today by bringing together the two stories piece by piece.
Structure
Scene in the Present for Narrator
Place the narrator in a specific scene in the present, e.g. a rocking chair on the back porch of her home, sharing her life story with a friend of relative. Intersperse her story with snapshots of the event as it unfolds, which will be the third-person story set in an earlier time.
Alternating POVs: Two Methods
These two stories will run parallel to each other.
Alternating Chapters
Perhaps one chapter is the narrator and the alternate chapter is the Event.
Structured Around Events
Or maybe you will organize the story around events, e.g. the homecoming of Ranjo's big brother in the caravanserai. In either case, the Narrator's Voice introduces, e.g. sets the setting or provides the information for, the next Event.
Fonts: Separating the Stories
To separate the two stories, authors sometimes use a distinct font for each POV, such as Franklin Gothic Book vs Arial or Times New Roman. Microsoft's Word Document has quite a few options. Italics can be difficult to read depending on a person's vision problems.
