Great to hear from you!!!
Families that work out together are a cherished thing. It can get tough when one child loses interest. I forget your children's ages but regardless, my advise is not to put demeaning pressure on them, such looking only at the next testing. It is a hard line to balance when you want your child to do an extra-curricular activity, that we know is good for them, but they do not want to participate. If possible, separate things like interest, comparison, logic/reason, even encouragement between the children. It has to be Her thing, not a group thing. One of the coolest things about MA's is that it's an individual practice we can do as a group.
When we meditate before/after class, I often tell the class to think on One thing they done really well and One thing they need to work on. The amount of information coming at someone, even children can get overwhelming. Help her slow down and stop worrying about the next test. It is only a valid goal when put in the correct frame. Remind her that when she learns the How in her techniques/drills/forms, the 'test' will come naturally. In other words, help her slow her pace and just practice the specifics. Get her doing the techniques she is good at and praise and encourage her. Then Help her with A technique she is struggling with. If you have mirrors at your school, they are excellent tools. People are usually very able to critique themselves. Plus, there is great tangential benefits that you, as a parent/teacher can glean from watching her, watch herself in the mirror. Things like posture, demeanor, expression, attitude are magnified. Continuously Talk to her (not at her) while she is looking in the mirror and explain what you see her doing. Most often, what you see and what she is seeing is quite different. Soo much information to be found there. Explain and Show her what you see her doing and how it is different.
Make her workouts, her workouts. Framing it only in the context that she is failing testing's is going to drive her farther away class.
One thing I have suggested to parents is to figure out who are her friends in class. Set up a play time with them outside of class. Sometimes making new relationships that are associated with the extra curricular (MA class) will be a motivator to keep someone working out. Over time, hopefully she will decide she wants to do MA for her own reasons.
Great to hear you are nearing your BB test. I would say some of the same things to you. 1st Dan BB testing only comes around once. Make is special and memorable. Even if that mean waiting a little longer so that you have the external stressors out of the way. The middle of a BB test is no time to be worrying about anything else, even your small child. I am sorry if that sounds harsh, but I hope you get what I am trying so say. The work that goes into prepping Everything to make your test 'perfect' is directly proportional to the reward at the end.
In every dimension, we do not have a clue to the craziness in each other life's. One thing I do on a regular basis is keep a running and ever changing 'to do' list. The better detailed and defined you can make your BB test list the better. Yes, expect the test will Not go as planned but still make a hard plan. This will help you figure out how to deal with the externals (like pumping

) that hopefully you can deal with.
Much the same, drill Only what you need as much as possible. Focus is the name of the game. Assess what is external chatter and what is internal necessity. You are already looking ahead, which is a good thing. Now, set down and put 'pen to paper' and work out a plan. This is a great tool to help focus your efforts.
Keep going and let us know how things progress. I wish the best for you and your children.