Hello, thanks for your question today! I am Dr. Drew, and I am a licensed veterinarian. I'll be happy to help you in any way I can.
Weight gain, and urinating blood, are issues that are not typically linked together by any particular disease,
but obesity is a risk factor for developing a urinary tract infection,
and hormonal imbalances, such as Hypothyroidism or Cushing's Syndrome, can both cause obesity as well as an increased risk of urinary tract infection.
the typical approach in such a situation, is a thorough physical exam, blood tests, and urinalysis.
x-rays or ultrasound might also be recommended, to check for bladder stones.
no, that's a highly unlikely explanation if she was spayed years ago.
mucus is common with inflammation in the bladder.
bladder stones would require surgery, in most cases. the other issues are managed medically.