I'm not sure you need to make any changes, unless the advisor is charging ridiculous fees or commissions. Preferred stock isn't like normal stock; it's sort of partway between a stock and a bond, and it typically pays higher yields, so the advisor probably chose it for the higher income and higher degree of security.
But if you want to feel more confident that the money will be there when she needs it, you can set up a ladder with individual bonds or CDs -- you'd put one year's expenses in CDs/bonds that mature a year from now, another year's expenses in CDs/bonds that mature in two years, and then a third year's expenses in CDs/bonds that mature in three years. That way you know you have living expenses for the next three years covered, plus it sounds like you'd still have another chunk of cash in fixed income in the event that she suddenly needs more (e.g., if she needs more support). And then each year as the CD/bonds mature, you use that money to live on and sell enough preferred stock (or use the income from that preferred stock) to buy another set of CDs/bonds that mature in another 3 years, so you keep that ladder going. The kicker is that if the market crashes, you don't need to sell right away, because you have three years' expenses covered, so you can wait until things recover to replenish the ladder.
tl;dr: your mom is doing fine. She has more money than she will likely ever need, the advisor doesn't appear to be bleeding her dry or putting her in ridiculously inappropriate investments, so don't drive yourself crazy. Research the kinds of investments she has, research the advisor and the fees, but otherwise don't let the perfect be the enemy of the good.