Of course, it varies heavily on the tone of the conversation, the level of intimacy and the overall mood, but these are possibilities :

• [Oui / Bon / Bref], et donc, tu disais ?

• Vas-y, je t’en prie[, je t’ai coupée]. (slightly more polite or formal)

• Non, allez-y, je vous écoute. (this one is even more formal, I just hope for you that you have a better level of intimacy with the lady… 😉

I used alternatively oui and non in the examples to make it a bit real, but of course it must match what the other person is saying at the very moment, as in these “little dialog wrecks” people tend to speak quite simultaneously, and without freaking Woody Allen filming it, what a waste.

Je dirais: “Mais pardon, je t’ai interrompue…”

C’est poli et suffisant pour indiquer que l’on souhaite reprendre la discussion là où elle a déraillé.