Help! Spitting!

My daughter aged 7 diagnosed ASD, won’t stop spitting. 

It has started all of a sudden 2/3 weeks ago and now won’t stop... it’s constant, when we’re out, at home, inside ANYWHERE and it’s driving me bonkers. 

I’ve been told to ignore it, but this doesn’t seem to be making any difference 2 weeks on and she’s doing it more, I’ve tried putting her inside her bedroom everytime she spits inside our house, but she just laughs and doesn’t care and will do it again as soon as she’s back downstairs. 

Has anyone got any ideas please?