If that portable Mac is your only backup, then a once-monthly backup schedule is courting disaster.
Mayo's Basic Rule of Thumb Regarding Backups: Decide how much work you are willing to lose, and then backup accordingly...
In the case of an active business a daily backup would be the minimum I would recommend, and I would backup to multiple sources, including a copy that can be kept off-premises in case of fire or theft. If that single folder is one large database you could also lose the data due to corruption.
You don't mention the kind of business your wife has, so ask yourself this question: what would be the cost to her business if she lost 29 days worth of data?