Ok just look up some basic sentences on google translate in Somalian, and learn them really well, like :
"Hello grandma, I'm really sorry but I can't speak Somali but I will still try and communicate" or "I'm learning Somalian with a tutor at the moment so it's still not perfect" (just lie) or something like that, at least so that she doesn't think you're dumb.
Secondly, I'm sure you're family aren't ashamed of you, it may feel like that in the heat of the moment but I doubt they think any less of you!! Good luck!! 👍