[mikemaccana]

Then use 'their'.

[sp332]

This particular (hypothetical) startup founder happens to be singular, and female.

[lawnchair_larry]

https://secure.wikimedia.org/wikipedia/en/wiki/Singular_they

[sp332]

That's the exact opposite of the situation. I pointed out that the founder is singular and female, but the "singular they" is used for indeterminate number and/or gender.