She might have thought it was a date. He did not.
Hence him taking her to a mortuary. He didn't give a flying foo fah about the impact this would have, thus confirming that in his mind, it was not a date, and that he had no romantic interest in her.
Their connection, was about their respective ishoos/attitudes in life. Especially once Milady SlutChops got involved, and they shared a common , enemy.
If there was any real flirting/chemistry going on, it was with ARAMIS.
..... and I reckon part of the Cardinal's problem with her, was that he wanted to boff her brains out too. But didn't have a hope in hell because of her intelligence, thereby wishing to dominate her in the only way he could, by stripping her of wealth/title/life.
I think all of the Musketeers wanted to save the 'damsel in distress', as part of their honourability.
But in summary :
ARAMIS WANTED TO SHAG HER, SHE WANTED TO SHAG HIM.
THE CARDINAL IS A DIRTY BASTARD AND HE WANTED HER TO WORSHIP AT HIS ALTAR.
THE END.