Your mother in law seems to be way smarter than you. The smart lady know how to take from both of the world. The conservative approach and growth approach both.
Here some info for you.
Debenture: Is not stock, but company borrows money from you at a fixed interest rate and every quarter or so they mail an interest earnings. When u buy debenture you are lending money to company to earn an interest.
But if the debenture is convertible, then after the period mentioned on debenture the debenture will be recalled and u get equivalent stocks. Mean while u already earned interest for few quarters. That brings yr stock purchase price lower than the market.