At a conference I was at, an agent said that they wanted a line included in the query talking about your next project, because she's going to be more likely to sign you if you have career potential. Should I add this line to all queries, or just hers?
Oh lo, we do find new ways to torture you don't we.
I can hear you all now getting back on your rodent wheels wondering how much to include; what if it's not the same category; but the next book is a sequel and you're not supposed to talk about sequels; what if it's a memoir and you don't have any more subject matter? Whirl! Whirl! Whirl!
Honest to god, I want to smack any agent who does this.
For starters, she's asking the question WAY TOO EARLY!
She's not going to know if she wants to sign you until after she's read the ms. Is she going to NOT read the ms because you didn't include a line saying you plan to work until the Grim Reaper comes calling, and if you can get wifi
Second, at this point, how can an agent not know how writers fret?
Oh wait, they're too busy telling you all the fucking hoops you need to jump through and making it clear that, but for writers, this would be a nice job.
Honest to Smut (and I mean the dragon-Smaug's younger sibling- not the category) agents like this should be required to be novelists for a year. They'd clean up their act pronto.
As to the answer to your question: add it just to hers.
You don't need the hassle of trying to work it into your query for the rest of us who have our priorities in the right order.
And when agents toss off those thoughtless little nuggets at writing conferences, you should all hold up signs to remind them that submission guidelines are to help writers and should be simple and easy. Not filled with little idiosyncrasies that aren't as transparent as the idiot agent thinks.