Does our dog have arthritis, torn ACLs, or neither?

I have a twelve year old Shepard/Husky mix. She is my boyfriends "childhood" dog and we took her from his mother about four months ago when his mother moved. For the past two months Kia (the dog) is having trouble walking. If she goes on any hard floor such as wooden or tile she loses her footing and does the splits with her hind legs or falls over while frantically trying to get up. I believe this is painful for her beceause when I try to help her up she either yelps or looks back like she is going to snap at me. She also crosses her legs when she walks sometimes and appears to be pigeon footed in her hind legs. When she pees she almost always sits in it from doing the splits while peeing or pooping. I have been looking for what this could be but cant find anything that matches her symptoms. I am looking for what this could possibly be because our regular vet doesnt have an x-ray machine. So, if I should go to our vet and get a referral first or just go to a vet with an x-ray machine first. does anybody have an idea what might be wrong with her?