Unslinky usually only posts on Teaspoon (which we all know is so rife with Rose/Doctor that it's really depressing going in there hunting for some Donna). Anyway, I found this story on there, and suggested she post on FF.net. Now she's posting the chapter up daily on FF.net (yay! not that I think it's cuz of my awesome powers of persuasion or anything, cuz it looks like she's been posting other fics up, too!), which is great because now more Donna/Doctor fans will find this story!
Jungle Adventures, by unslinky - https://www.fanfiction.net/s/10005470/1/Jungle-Adventures
Warning: There's some pretty explicit stuff going on
You should totally go read and then if you're feeling adventurous, leave a review, because I think Unslinky is slowly converting to the dark side (and by dark side, I mean Ten/Donna - the black sheep of Doctor pairings) and a little push in the that direction is always welcome. ;)
Also, her "Call Martha" series on Teaspoon is adorable: Doctor whump, Donna sass, Martha to the rescue. It's written as DoctorDonnaFriends, but I read UST into it. BECAUSE IT'S THERE, GOSHDARNIT, IT'S ALWAYS THERE! Here it is: http://www.whofic.com/series.php?seriesid=4027 (ehem, yeah, Jungle Adventures is complete on here, but I still say if you're going to review, do it on FF.net so she'll continue to post there! That moderator-approval thingy on Teaspoon is just a killer.)
Happy reading if you haven't before!