She doesn't sound like a native speaker to me (unless she has a regional accent I'm not familiar with and in which that pronunciation is common). As far as I know, pretty much every variant of English pronounces it as if it starts with "stum". Hers starts with "stom", as if she is someone who is used to pronouncing words phonetically.
At the risk of boring you with the same message over and over again, please use Forvo! You don't need to guess whether someone is a native speaker or which variant they use. It's clearly shown by their username. You can trust the pronunciations on that site!
I opened the video but I didn't bother skipping on to the relevant time. In the first 30 seconds, she mispronounces "pronunciation", saying "pronounciation". As far as I'm concerned, if she can't even get that right, there's little point taking any other advice from her.
Edit: I listened to the first 90 seconds of the video. She's clearly not a native English speaker. She makes the same "o" error in "other" (I mean the same error she made in "stomach"). She pronounces it as if rhymes with "bother". It doesn't. My guess is she's either Scandinavian or possibly from somewhere in Eastern Europe.
I simply said what the website says. The website says "Nationality - Belgian. Languages - English, French, German (native)". I take it that she's written it herself. Doesn't nationality suggest where she's from?
I take it all back. Apparently, the three official languages of Belgium are Dutch, French and German! I honestly did not know that. I thought they were Flemish and French! So yes, it appears she grew up in the German-speaking part of Belgium.