We spoke on (date here) when you came to our institution and presented
on (topic here). I very much enjoyed your speech and our discussion
afterwards on (a few words on what you talked about) and possible
openings in your company. As discussed, I've attached my cover letter
and resume for your consideration.
Thanks so much, and I look forward to hearing back from you!
(Your name here)
My post is making the email a bit less formal, as I assume you talked to her in an informal way. By bringing up where you guys were, when you met, and what you talked about, you're likely sparking her memory (unless she gave two talks and had identical conversations that day, which is unlikely). I'd also keep the email relatively concise, because your intent is to seek jobs, not make a new friend.
Personally, I would attach my cover letter, because the cover letter gives a better indication on not only what your skills and past experience is, but also on what your desired position is. It also gives the employer a bit more indication into what you're like as a person, and whether or not they'd want to hire you.
This is all, of course, assuming you're emailing her and not mailing it. If you mail it, I would put a shorter version of this email into the cover letter and only send the cover letter and resume.