Can someone please advise me as regarding fixed-rate annuities?

My mother-in-law, who is 81 and in excellent health, has close to $300,000 in investments, and may wish to invest around $50,000 of it in an annuity. However, I know rather little about the subject, and therefore feel unqualified to advise her.

The chief reason for her desire to invest in an annuity is to achieve tax dererral. However, she is not in a high tax bracket; and I don't know how this tax advantage would hash out against, say, the surrender charges and other fees of an annuity.

Can someone offer any facts and/or suggestions?

Thanks.