Love's Guardian, by Dawn Ireland

Declan Deveraux, the Earl of Worthington, is a man
who knows one thing for certain – he will never marry
for love. With that aim, he pursues only the most vain,
and spoiled, women of the Ton. Fate has other plans for
him, however, and he’s made guardian to Alex Kendrick,
a female he likes – God forbid. Now Declan has to get her
suitably married, before he succumbs to the temptation
to make this fiery temptress his own.

Alex, a rapier-wielding countess in her own right, doesn’t
welcome a guardian and crosses swords with him at every
opportunity. In spite of their less than auspicious beginning,
she soon discovers Declan’s quick wit and Black-Irish looks
inspire an emotion she can’t ignore, love. Now the battle is
for Declan’s heart, because Alex will accept nothing less.