So, more info for those following along. I'm not sure why I'm posting this, perhaps as a way to organise my thoughts or perhaps to help someone else (hopefully not) that has to navigate this path in the future.
Mast cell tumor are grading using two systems : the 3-tier Patnaik system and the 2-tier Kiupel system
Ella's tumor was graded as low under the Patnaik system and "hmmmm we're not confident grading this" under the Kiupel system. The reason for the uncertainty is the Kiupel system only grades as high or low (no in between) and is based on the Mitotic rate. A rate of 7 and above is considered high. Ella's sample was rated at 6.
The oncologist weighed up all of her observations and experience and has diagnosed it at high grade.
However, we have sent the sample off for additional testing. I didn't quite follow this part but I think the original testing captures one snapshot of the tumor and might not reflect the tumor as a whole. It's expected that this additional testing will confirm the diagnosis as other areas of the tumor are likely to show the higher Mitotic rate.
There is one glimmer of hope but I'm trying not to think about it too much. The oncologist asked us to look back through our photos of Ella and focus on the spot on her nose and when the first signs appeared. As it turns out, you can trace the tiniest changes to her skin (next to her nose) all the way back to June last year. (as an aside - I won't allow myself to think at all about this and any ifs or maybes - I don't think I'll cope). The tiny glimmer of hope is that nearly 8 months later, Ella doesn't show any symptoms of metastatic mast cell cancer, which is unusual. Of course that doesn't mean it hasn't metastasised.
Finally, for those following along, the medication Ella is on is called Palladia. It's an "oral receptor tyrosine kinase inhibitor (RTK inhibitor)". Of course it's most effective when combined this chemo but still useful on its own. I'm glad we still have our insurance as it costs $900 per month

. She's been on it a couple of weeks now and thankfully has had not visible side effects. She's still happy, hungry and still doing daily zoomies
Will report back when the test results are in.