Oh yeah, the blue fates are the acquainted...
Those ones you can spend anytime, but don't buy any with primogems.
Since you can get any standard 5* there, character or weapon, that means you have an equal chance to get one out of fifteen options. Not ideal to get Keqing specifically.
On a character banner, it's 50% for the character in question, but if you don't, the other 50% will always be one of the five 5* standard characters and never a weapon. So technically, you have a much higher chance to get Keqing there, even if you are "unlucky" (or lucky in this case then?).
I'd say play the game, roll on a character banner if there's someone you really want and maybe you'll get Keqing (and say, if you actually get a 5* but not Keqing, so instead you get Diluc/Mona/Jean/Qiqi, you'll be sure 100% sure to get the next character banner, including Keqing if her banner comes back).
Speaking of current banners, Shenhe is probably not a good option if you don't have the characters she really supports, that is Ayaka and Eula.
Xiao is a decent DPS but not the best, though he does go very well with Jean. Where did you get Jean and Mona by the way? I know the games only tracks the last six months of rolls... maybe you got one on a character banner but it doesn't appear in history anymore?