When they are that small they can / will eat Fruit flies, roach legs or cricket legs, she could take down a tiny pinhead cricket.
What I like to do when I have only one or two tiny slings. I'll leave a small slice of fruit out and collect a few maggots from fruit flies. They eat them right up.
The only pinheads I can pick up local, you have to buy a box of 30 (so that's a waste) a whole culture of fruit flies is a waste too. I'll also toss them in a leg here and there. After a few feedings it will be able to take down a new born roach.

Here is one about a year old now.


They make great first Ts