A word group that begins with although cannot be linked to a word group that begins with but or however. The result is an error called a mixed construction (see also S5-a). Similarly, a word group that begins with because cannot be linked to a word group that begins with so or therefore.

If you want to keep although or because, drop the other linking word.

If you want to keep the other linking word, omit although or because.

but she has written several books for children.

For advice about using commas and semicolons with linking words, see P1-a and P3-a.