A search on Ancestry using England and Scotland Select Cemetery Registers 1800-2016 revealed a burial for her in Chingford Mount Cemetery on 26 Feb 1903 in Section G10, Grave 61777 and internment 61866. The transcript gives very little detail than that quoted above, so I wanted to find an image.
There are actually quite a few pages that have been missed. They ARE there as you can see the page numbers showing through, they just haven't been included.
I've had problems with missing pages in this dataset. I found a workaround that works in most cases and has done for Gertrude.
The method is to go to the image for the nearest page, then manually edit the URL adding (or subtracting) 1 to/from the image reference in the URL to get to the next page.
Gertrude's record is on the left hand side page of folio 145.
The manually edited URL reference number for that image is 46493_3082375_0013-00
199(digits in red are the ones I had to change)
- however, I'm using the library edition at the moment so the URL format might be different on other versions.
When viewing that image the viewer claims it is image 2147483575 of 272.
Gertrude's address was given as Margaret [St/Sq] Hackney.
The entry immediately after hers with the same grave number appears to be for an (unrelated?) baby.
Edit: and there are further burials with the same grave number on the 27th.