Seems to me that she just fukked herself over for future financial interactions with the father who gave the money. Yeah, it's her money now, but would it have been difficult to say, "hey, those other two won't have anything because their fathers won't step up, so I'm going to use the money for all three. I really appreciate you coming through for us". Just seems like going behind his back and him finding out was just being dishonest.
To all the people talking about "well he should have taken him shopping personally", maybe he thought his bm was trustworthy. Excuse him for thinking that she was honest and upfront. He definitely won't be making that mistake again.