I can't imagine having my mom stay with me like that. Seems like it should be private for you to enjoy too. It's your baby too. I wouldn't have my privacy invaded like that. Breastfeeding is hard though. I remember crying alone in a room by myself one day with my shirt off. I gave up, so don't listen to me. I wasn't as dedicated to the idea as I should have been. I regret it now though. :/
I wish I could say something to make you feel better. If it were me, I'd be pulling my wife aside and telling her that mom has to go home or has to stay in a hotel. I wouldn't have accepted a situation like that in the first place. Can she stay in a hotel in the evenings?