My 3 and half month old dobe vomits deliberately.. or should I say, 'regurgitate'?

She's done it twice in 2 weeks... there seems to be no apparent reason for it..

The first time. She woke up in the mornin, and started acting like she was taking part in a burping competition.. she was deliberate trying to eject the contents of her stomach. After about 10 or so burps, she puked white yellowish liquid and she tried eating it again when I stopped her..
She did this act 3 times..

She didn't seem to be in pain.. she looked quite comfortable doing it..

Today she ate puppy food in the mornin and soon after she took it all out in the same fashion and tried eating it again..
It reminded me of my Rabbit which used to regurgitate for her little ones to eat..

My friend says puppies do it when they feel uncomfortable and there's absolutely nothing to worry about..

Btw could it be a sign of gastric tortion? Its quite common with dobes and danes isn't it..