How can a single woman be a "keeper" of the home?

In Bible times, we do not see much of the idea of single women dwelling in houses alone. We can assume that it happened occasionally, but a single woman would normally be part of a larger family unit. In Psalm 68:6God setteth the solitary in families: he bringeth out those which are bound with chains: but the rebellious dwell in a dry land.
See All..., we find that "God setteth the solitary in families." Those who are solitary (alone) are put into families. A single lady might stay with her parents or work with another family. Either way, she could certainly help with the keeping of the home.

It is possible that you are thinking of single mothers. I do not believe that the "keepers at home" phrase of Titus 2:5To be discreet, chaste, keepers at home, good, obedient to their own husbands, that the word of God be not blasphemed.
See All... prohibits any sort of working outside the home. Certainly, there are cases where a secular job is absolutely necessary. I believe that the ideal is for the mother to keep the home without an outside job, but sometimes we see preachers coldly pushing this ideal on many who do not have ideal circumstances. Most of the time, he only makes the single mother feel guilty. Or worse, he may create an unnecessary rebellion in her heart. Staying at home is a conviction God must give and a provision He must make. However, I have seen ladies that really had to work outside the home bring up godly children. They did the best they could and God made up the difference.

But even in those circumstances where the single mother or woman must work, she can still be the keeper at home. Even stay-at-home-moms do not stay at home all the time. They are not imprisoned in their homes, yet they are keepers at home. In the same way, a single woman or a single mother can keep the home when she is there. God will be pleased and He will bless her efforts.