I really like these dialectical variations cropping up, it's better practice for understanding native sprakers :)
Is this correct - wouldn't this be in present tense? "she is coming tomorrow"
It would be Bydd hi for she will?
This is a dialect variation - the use of am to indicate a future intention. More often, am is used with a verb-noun to indicate wanting to do something:
- Dw i am fynd i'r siop - I want to go to the shop
- Dw i eisiau mynd i'r siop - I want to go to the shop
I think that it might be quite a local dialect variation, though. If we find that it is very local and not often found outside a particular area then we may perhaps drop it from the course to remove any confusion - there are many examples of more common variations that we do not include at the moment.
However, it is a good example of much variety there can be in the language.