My advice is to tell her that her contract is direct with you and that rent must be paid up front - RA is normally paid in arrears & causes problems when the tenant moves out. It is possible to get the chq made payable to you and for her to pay the balance, but she must ask them to do that (unless it has changed in the last few years).
Other than that, hopefully all will go well, I often find this set-up (single mum + child) makes an ideal tenant as they are really looking to make the place a home - rather than a group of professionals who often go their separate ways.