Is it a coincidence that since male cat died our female cat keeps urinating?

[scraggy]

Very sadly our male cat died about a month ago and since then our female cat has been understandably very quiet. However, about a week after his death she started urinating in the house. She is an outdoor cat and normally urinates outside, she has easy access to the catflap. I am worried that she may be depressed and I am wondering whether I should get another cat to replace him to keep her company. Can anyone help please?