I am so sorry about your poor dog.
Lomustine and prednisone are both a bit immunosuppressive. She may just have a urinary tract infection. UTI's can be brought on by stress, such as being boarded. It may take her a bit longer to get over the infection due to the Lomustine, prednisone and the lymphoma.
She seems to be feeling a little better, however her legs are still very weak. She went outside this morning and could not stand after urinating. We had to pick her up into a standing position and when she is standing she can walk well. It is getting up that is hard. We also noticed that her abdomen has been a little hard for the past few days, but she is still eating and excited about food and she is drinking lots of water. I know lomustine can cause liver damage and the cancer did spread to her liver before, could that be what is happening? We would be worried about bloat, but other than her weak legs, she is not acting overtly sick. Not any more sick than before the infection a couple of weeks ago, when we found out her cancer was back. Plus, it has been like this for a few days and her condition hasn't changed - if anything she has gotten better. Rushing to the vets for treatment wouldn't do a whole lot of good because she probably won't live much longer due to the cancer anyways. Her last dose/first dose of lomustine was 2 weeks ago and we've decided to discontinue the lomustine given her current state. $5,000 later, we tried to do everything that we could and it wasn't enough. If we noticed her acting extremely distressed, we wouldn't think twice and we would put her to sleep. But she seems to be in good spirits. What could cause her hard abdomen and weak hind legs?
Thank you for your help. This is definitely not an easy situation.