My mom knows I've been struggling (though I live on my own) because I went from a $28/hr job to $11.50/hr! I've got bills to pay, car to acquire, a dog to look after, and food to buy - so I had to straight up tell her what I've been doing.
I made it into a bit of a joke (my mom is probably more open than most) and told the the funny aspects so she doesn't worry.
"It's fine, I don't have to do anything I don't want to. Some guy gave me $5 to put on a pair of high heels, and someone else asked me to spit in my hand haha!"
I made light of it, even though I had also masturbated on cam and have made a fair amount of money for doing it.
She had concerns about privacy - so I explained that I signed on with the biggest website, use a different name, and tell people I live someone I don't actually live (but in the same time zone to avoid confusion)
She also had concerns about me being belittled or what if someone she knows is on one of those sites looking at me?
You should have a serious talk about it with your mom, ask her to ask questions, and be as honest as possible within your limits! Address her concerns and be very understanding of her feelings.
Also, it helps to have a part time job as an excuse!