My dog is having trouble walking

Hey guys, I am needing some advice about what could potentially be going on with my dog. I am planning on taking her to a vet tomorrow. To preface, about 2 years ago she partially tore her ACL or another ligament in her rear, left leg. I had x rays done and a sedated exam but the vet was not 100% sure what was going on, and advised to keep her on bed rest and monitor for further tearing. She also has double jointed back legs so they are hyperextended and the vet told me she will definitely have arthritis when she is older because of that. Fast forward to this past monday, I was feeding her and she got up to run to her bowl. She immediately yelped sat down, and started limping. A few minutes went by and she was okay and walking normal again. Tonight, she jumped off of my bed. I let her on it, because I bought her stairs and was trying to teach her how to use them. Immediately she started panting, crying and pacing around the room. She is not putting any pressure on the same leg that she had issues with 2 years prior. She is having a hard time getting comfortable. Ive given her some doggy aspirin and put her in her kennel to try and keep her from jumping on and off things for the rest of the night. I was wondering if this could be arthritis setting in, or if it sounds like her may have fully torn her ACL or another ligament in her leg. Or if this sounds like something completely different.