According to COCA, bachelorette is more popular than spinster (and unmarried woman), something that only really changed in the last 10-20 years. Compare the "per mil" rows in the following charts.

Spinster:

Bachelorette:

Unmarried Woman:

One pretty significant thing I see in these charts is the fact that most of the hits for spinster are from fiction (and there are very few hits for the other sections).

It's also important to note that spinster is not neutral:

The development of the word spinster is a good example of the way in which a word acquires strong connotations to the extent that it can no longer be used in a neutral sense. From the 17th century the word was appended to names as the official legal description of an unmarried woman: Elizabeth Harris of London, Spinster. This type of use survives today in some legal and religious contexts. In modern everyday English, however, spinster cannot be used to mean simply ‘unmarried woman’; it is now always a derogatory term, referring or alluding to a stereotype of an older woman who is unmarried, childless, prissy, and repressed
_{Oxford Dictionaries}

According to COCA, bachelorette is more popular than spinster (and unmarried woman), something that only really changed in the last 10-20 years. Compare the "per mil" rows in the following charts.

Spinster:

Bachelorette:

Unmarried Woman:

One pretty significant thing I see in these charts is the fact that most of the hits for spinster are from fiction (and there are very few hits for the other sections).

It's also important to note that spinster is not neutral:

The development of the word spinster is a good example of the way in which a word acquires strong connotations to the extent that it can no longer be used in a neutral sense. From the 17th century the word was appended to names as the official legal description of an unmarried woman: Elizabeth Harris of London, Spinster. This type of use survives today in some legal and religious contexts. In modern everyday English, however, spinster cannot be used to mean simply ‘unmarried woman’; it is now always a derogatory term, referring or alluding to a stereotype of an older woman who is unmarried, childless, prissy, and repressed
_{Oxford Dictionaries}

According to COCA, bachelorette is more popular than spinster (and unmarried woman), something that only really changed in the last 10-20 years. Compare the "per mil" rows in the following charts.

Spinster:

Bachelorette:

Unmarried Woman:

One pretty significant thing I see in these charts is the fact that most of the hits for spinster are from fiction (and there are very few hits for the other sections).

It's also important to note that spinster is not neutral:

In modern everyday English, however, spinster cannot be used to mean simply ‘unmarried woman’; it is now always a derogatory term, referring or alluding to a stereotype of an older woman who is unmarried, childless, prissy, and repressed
_{Oxford Dictionaries}

According to COCA, bachelorette is more popular than spinster (and unmarried woman), something that only really changed in the last 10-20 years. Compare the "per mil" rows in the following charts.

Spinster:

Bachelorette:

Unmarried Woman:

One pretty significant thing I see in these charts is the fact that most of the hits for spinster are from fiction (and there are very few hits for the other sections).

It's also important to note that spinster is not neutral:

The development of the word spinster is a good example of the way in which a word acquires strong connotations to the extent that it can no longer be used in a neutral sense. From the 17th century the word was appended to names as the official legal description of an unmarried woman: Elizabeth Harris of London, Spinster. This type of use survives today in some legal and religious contexts. In modern everyday English, however, spinster cannot be used to mean simply ‘unmarried woman’; it is now always a derogatory term, referring or alluding to a stereotype of an older woman who is unmarried, childless, prissy, and repressed
_{Oxford Dictionaries}