I mean, we could see it as an enthymeme. One option to reconstruct an argument is:
(1) If you're not willing to take them in, willing to sell all your possessions and bankrupt your family to provide for homeless people then you're not helping them.
(2) If you're not helping then you don't act according to your claim as well.
(3) If you're not acting according to your claim as well then the claim is wrong.
(4) You're not willing to take them in, willing to sell all your possessions and bankrupt your family to provide for homeless people.
(C) Your claim is wrong.
I had to really bend it into shape to even address the claim of B. So if that's not what the person implied then they simply don't pose a relevant argument. It's possible that they just don't care about ethical claims at all and simply want to make B feel bad.
But if it is what they implied then we could demolish the argument at multiple points. Let's just grant premise 4. Premise 1 and 2 are factually wrong. But the main problem is premise 3. It's just not true whichever way we put it. I guess we could call it "whataboutism" or "tu quoque", but obviously we would have to explain to A that there's a premise which isn't even slightly plausible instead of just yelling fallacies.
edit: Oh yea, about the headline question. I guess such cases sound like "tu quoque". But it's not necessarily the case.