It is not too late to spay. She shouldn't be at anymore risk than a puppy as long as her preop tests are normal. My girl was spayed at age 6 and did just fine...
Unfortunately, the risk of cancer will be the same whether she is spayed now or never. The window of preventing mammary cancer is over. However, she wouldn't be able to get uterine cancer. It would prevent pyometra which is very important. She may still hump. It's now a learned behavior.
I would have your girl spayed.
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