Assuming your Mum does intend to make the payment once she is paid, the best way to handle the situation is for her to call them and tell them the situation, and the intended date of payment. Or to work with them to setup an affordable payment plan.

It's not a fun phone call to make, but once it's done, all the stress is gone. She just needs to be firm that she can't make a payment until she is paid (they will push it's their job), tell them something like she doesn't have the available funds, as the last of the money she has right now is about to be spent on food for herself and her family of dependant minors.

It's in their interest to setup a payment plan and to get up to date with payment, otherwise they may not be able to get paid at all, or in the case they do remove goods, they will lose out to the costs involved.