Drawing the line on 'contact'???

[WyMike]

First year working BB and I'm having trouble with this scenario. This happened a number of times in a 7th grade girls game over the weekend:

A1 is bringing ball up from the backcourt into frontcourt with B1 running along A1's left side in the same direction. A1 has her left arm up but not out in a flagrant "guarding the ball from defender" attempt but still a marginal shielding type of move (which I guess is very prevalent in young girl games?).

B1 reaches over A1's left arm without contacting the arm and tips the ball away. After the ball is loose A1 and B1 make shoulder contact and both stumble and go to ground. Is this a black and white 'pushing' foul on B1? What if they don't go down but contact is still made?

I think I should be calling these closer but with the contact these young girls have with their general playing overall, I get the "Incidental Contact" feeling from working football playing into my head. Certainly you cannot call each and every contact a coach hollers for, can you? Anyway, I'm having a tough time defining the line of when to blow the whistle or not on a 'steal attempt' with contact...