The work thing should be fine, just explain it clearly that the money was basicly reimbursement for expenses she covered and if possible show the receipts or the PO/invoice for the items if needed.
The cash under the mattress they may not allow to be counted if you close within 2 banking periods of that deposit. The explanation for the deposits will still be needed and it will be up to the UW whether or not they allow that $ to be used. They usually only wil count deposits with some sort of paper trail to prevent someone from loaning you the money, etc.
