Take all the time you need, be patient, a break is good to remove yourself from this toxic situation.
You will eventually have to face her again at the wedding and love your son.
But don't sink to her level of personal insults, remain sober, and try, as hard as it may be to remove your emotions from reason. Stand firm, if she gets all riled up or interrupts, say, "don't interrupt me while I'm speaking." You can stand up to her and for yourself as long you take that time you need to remove yourself from the current situation and gather yourself. try not to take things she says personally, especially lies or insults. Don't let it get the best of you, instead remain calm and steadfast, don't let her doubt yourself.