Vanguard is good. They have low fees and lots of investment options.
If you roll over to a Roth IRA, your mother will need to pay tax on the entire amount this year, and all the withdrawals will be tax-free. If you roll over to a traditional IRA, no tax is due this year, and she will owe tax on any amount she withdraws in the year she withdraws it.
If you wish to wait until after the election to put the rollover into the stock market, you could park it in a money market fund for a while. This is like a savings account: the money will earn some pitiful amount of interest, losing ground to inflation, but the number of dollars you have won't go down.