we also breastfed. my lo went thru a short time of STTN for about 2 weeks around 5.5 months but then he started waking again

. he woke around once a night. anyway, he started "officially" STTN at 8 months. i was also kinda sick w/ a bug at the time and so Dh was on nightshift duty. i think my Lo was waking out of habit. i worried about him starving in the middle of the night but i really think it is just a behavior issue at that age.
i started DF very early on and it helped some. i don't know if i would've started it at 7 mo. is your LO waking more/less with the DF? how long have you tried it? it can take a while for it to kick in and it doesn't work for all.
another option is to slowly decrease the amount of time she BF during the middle of the night. if she takes a bottle, you could try offering one w/ diluted BM or formulaor water, as mentioned. better yet, have your hubby take over the nightshift on the weekend and responds to her NWs.
i agree w/ one of the PP, sometimes it was just easier to feed during the middle of the night (when you aren't thinking clearly) which is another reason to get your DH involved!

i totally understand your frustrations. i hope she STTN soon!