I would want to know why that child is struggling. Is she just being lazy or is there a real problem? Is the material too difficult or were the basics not well-learned? If there's no real reason, then look into ways to just get through it together! There are plenty of subjects that I don't care for, and I try to not project my attitude to my children. Maybe they'll love algebra!
We pretty much repeated 4th grade math because we changed to a different curriculum that didn't work. I switched back mid-year and it worked out much better. We're doing the same thing this year with Latin because I don't think my daughter learned the basics well enough to move on to a translation curriculum. My daughter has done Prima Latina, and Latina Christiana I and II, but we're doing First Form Latin instead of Second Form because she's just not ready to move on yet.
While there are many "tricks" to making learning fun, sometimes, you just have to do the next thing. Mix up the tasks, the schedule...Do that least favorite subject first to get it out of the way and make more time for the fun stuff.
That's the great freedom of homeschooling. You know your child and can best accommodate the needs of your children. I love setting the schedule that works for us and using the materials that best fit each child.