So, uh... I just so happen to know that you can buy capsules of liquid blood. You just pop them in your mouth, bite down, and... blood. Mixes with your saliva to produce a whole lot more than you'd expect. Used them for a Halloween costume one year.
Use this knowledge as you wish. ��
First, kudos to you for being such an amazing person! :)
Second, this type of product comes to mind: https://www.amazon.com/Fun-World-Liquid-Blood-Capsules/dp/B00I5RIONK. I've seen things similar to this used for theatre productions ("getting a punch to the mouth", etc.), as well as Halloween costumes (as the product suggests). If she gets a pack, she'll need to hide the extras, but she could also practice/mess around with them to see how easily she can break them, etc.
Hopefully that helps!
I've made this before, really easy: http://www.instructables.com/id/No-Cook-Edible-Fake-Blood-for-mouth-wounds%2C-etc./
And totally safe to be in your mouth.
Edit: here is a premade solution in convenient capsules: https://www.amazon.com/Fun-World-Liquid-Blood-Capsules/dp/B00I5RIONK