How should I plan retirement for 48 y/o with less than 2k salary?

Firstly, ensure that she has a basic level of guaranteed income when she retires by ensuring that she has CPF contributions. CPF Life is one of the best annuities around and it gives a lifetime of income. As we do not know how long we live, a lifetime annuity forms the basis of 'survival income' to ensure that she will has money for essentials. You can also contribute to her SA (up to the prevailing FRS) when you start working so as to enjoy tax relief and help her retire better. Once she turns 55, you can contribute to her RA.

Do note that this is a one way traffic however, money put into SA/RA will largely not be able to be withdrawn.

Next, ensure she has medical and Long Term Care coverage. Medical and nursing bills cab be quite hefty and we want to ensure that such bills do not drain us of money for retirement. Beyond Medishield life and Eldershield, look at getting an integrated shield plan as well as Eldershield enhancement.

Once those are taken care of, we can look beyond the basics. Creating lasting income from both guaranteed and variable sources will ensure diversification across various asset classes (retirement plan, equities, fixed income, etc) and a stable, low volatility portfolio. The exact composition of such a portfolio is dependent on your mom's risk appetite and preferences, so discuss with a consultant who can help you to plan and allocate her limited resources accordingly. Retirement saving plans from the banks would be an option but it is important to compare with other insurer plans as the banks only distribute products from a single insurer, so as to ensure that she gets the most for her money.

There is a sequence to financial planning.

Before even looking at interest rates, retirement savings plans, insurance, investments, perhaps one should take a step back and look at their financial health.

A few simple ratios to consider if one is financially healthy. Savings Ratio, Total Debt Servicing Ratio, Emergency Fund. All the ratios should be looked at in totality just like how you read a blood test report. Are you serving too much debt based on your income? Have you set aside an emergency fund of about 3 to 6 months of your expenses?

Once all that is taken care of, you should look at a systematic and organised way to save and then invest by means of a budget. Identify your fixed and variable expenses, look at how you can reduce some of these expenses in order to have a surplus.

From this surplus, you can now look at protecting this human capital. The role of insurance in your financial plan is for protection against the loss of income. Loss of income would mean you are unable to work towards your financial goals (Retirement).

What could cause your financial plan to fail? When your income stops permanently or a very long time, you have no choice but to draw from your current assets to fund your current lifestyle and that will affect your ability to reach your goals. Death, disability, and major illnesses could cause your plan to fail. Insufficient returns could also cause your plan to fail. That is where the right types of insurances and investments come into your financial plan.

As Luke rightly pointed out. Retirement is a vague word, what does it mean to you?

Perhaps a better term to use would be Financial Independence, or having a fully paid roof over your head, and a sum of money sufficient to pay for your expenses until you die. (CPF LIFE would form a good foundation for you to build upon, depending on the standard of living you desire)

Insurance is an expensive way to save/invest. There are many low cost investment options in the market today. You are not just limited to the banks when it comes to financial planning. Seedly is a fantastic platform with a wealth of information on personal financial planning to help you make better decisions :)

I'm kind of surprised that no one has pointed out that retirement is tremendously subjective.
If your mum is a pretty simple person who doesn't need a particularly high standard of living, CPF could literally be enough by 65.

If she wants to retire before that, it changes the whole game. Or if she wants to retire at 70 instead. You get the general idea.
So whether or not she has less than a 2k salary is not as important as how much she's saved already and how much she's willing to save, depending on the kind of guaranteed income she wants in retirement.
The instruments and risk required to meet those goals also vary depending on some of the stuff I mentioned above.
You may want to edit this post to include some of these points so that people can give you more detailed advice.

7 yrs to 55 year old. If the flat is already paid-up, after putting aside about $50,000 cash as emergency fund, move the rest of the cash to SA. Also move the OA to SA. Take it as a 7-yr fixed deposit at 4% interest. At 55, if there are more than the CPFLife amount in both the OA and SA, balance can be withdrawn or leave in cpf to earn interest.