Will an injured cat stop using the litter box altogether?

My 11 yr old cat somehow got injured jumping off the mantle, and I think a small potted plant may have fallen on her paw. It's swollen and she's limping. The same day, I took another cat of mine to be spayed, and my dog ripped a pad off his paw, both of which tapped me out financially at the vet, and therefore I have no money to take her to the vet, who wouldn't offer me any help even though I've been a customer for over 10 yrs. and have always paid in full. Anyway, I noticed the swelling went down, but she's still limping. She's eating very well, though, but I haven't seen her go to the litter box at all. I have 3 cats total and I'm keeping it clean as always. I tried locking her in a separate room with her own box, so I could monitor her use, but 4 hours later, nothing. She may be going at night, but it's hard to tell with 2 other cats in the house. Is it possible that the trauma of her injury is preventing her from going at all? Or could she be picking up on my stress because of what happened to her and the other 2 animals all in one day? This happened 2 days ago...would she be exhibiting signs of illness yet from not going? I'd be extremely appreciative of anyone who could offer any help...I'm unemployed and freaking and feeling like an awful parent. I won't be able to muster up the money to get her to the vet till next week....