Firstly, and importantly, do not mention anything about her helping your wife with the baby. It'll raise a red flag and create extra scrutiny by the caseworker.
Secondly, there's really nothing you can say regarding taking any responsibility/action for sending her home etc. It'll be completely ignored.
The caseworkers and ECO's will form their own views on the application presented based largely on the reasons for returning home outweighing those for staying beyond the visa expiry.
Return tickets do not show any intent to return home.
Without strong ties to her country it's going to be a weak application and based on what you've shared there doesn't appear to be any ties.
The cost is low and decisions get made fairly quickly.
Always worth a punt, especially when family members are involved together full sponsorship.