What the F?

Yesterday I sent a letter notifying an author that we’d decided to accept her manuscript for publication. This morning I opened my e-mail to a message from her:

Thanks for the f/u.

Does anyone know what "f/u" means? I assume she’s not thinking I told her to fuck off, because I gave her good news. However, she does live in Jersey, where manners are lacking.

Thanks, kind regards, best and f/u,

Sara S.
Editorial Assistant