Before drinking the sotah water does the woman make a blessing? If so would it be shahakol or something else?
Sefer Otzar Palos HaTorah pg.161 brings down that no birkas hanehenin is said on Sotah water since it has a bad flavor.
Rav Chaim Kaniefsky rules that one does not make a birkas hamitzvah on Sotah water. He brings a proof from Berachos 51b which says "one does not make a bracha on calamities".
It is also noted that the Sotah who knows that she is innocent still won't say a beracha on the Sotah water since her predicament only came through suspicion of aveirah. This is like the Rashba (Shu"t §18) who holds that one does not make a birkas hamitzvah on something which came through a sin. (‘Taama D'krah’ by Rav Chaim Kanievsky - Parshas Naso).
You only recite a bracha on water if you are thirsty.1 Since the sotah is not drinking the water to quench her thirst, there would be no bracha. As for birkat hamitzvah I don't know.
The question has been raised in the comments about what if the sotah was thirsty when she drank the water. It seems (at least in the way I interpret it) that according to the Mishnah Berurah, she would recite a bracha.2
1 Shulchan Aruch, O.C. 204:7. Borei Nefashot would not be said as well. See also Brachot 44a and Rambam Brachot 8:1.
2 Mishnah Berurah 204:2. The case is drinking water in order to swallow a pill. If the person drinks the water in order to swallow the pill and to quench his thirst, according to this opinion he would recite a bracha on the water. Perhaps if the sotah was thirsty, she would recite a bracha as well.
שאין מברכין על הקלקלה כמו שאין הכהן המשקה את הסוטה מברך
we don't make a blessing on something negative (lit. "cursing), much like the Kohein who administers the drinking of the Sotah water doesn't recite a blessing.