Oh poor Chloe and poor you. hugs.
Some problems, especially back & neurological problems can come & go like you described. Of course with any major problem like that you will be seeing more bad days than good, generally speaking.
X-rays are a good first step, as is bloodwork (ask them to do it when they do the x-rays). A specialist is a great step to take after the x-rays have been done, depending on the results.
Sounds like she's been through a lot of change lately. There is a possibilty that some of her "not acting herself" may be caused by that as well as whatever is going on her medically. Make sure she has safe places to go to when she feels threatened but make sure she has plenty of her own special time with you & the family as well.
Good luck & keep us posted.
How old is she again?