3 year old collie mix having accidents in the house?

My three year old collie mix has recently began urinating and defecating in the house. She was fully house trained previously. We got her as a rescue about a year and a half ago. She is crate trained, however we stopped using the crate about 8 months after getting her, as she was able to be out of the crate without displaying bad behavior. She has urinated and defecated in the house about 7 times since Easter...I thought maybe a urinary tract infection, but it doesn't seem to happen regularly and she also defecates. She knows how to ask to be let out and we try to keep her on a schedule so she knows when we will be home from work etc. Any suggestions or thoughts?