She will invite other cats, dogs, the Amazon delivery man, anything that might have a penis to get it on - if you have a son or husband, they'll see a lot of her rear quarters.
Usually, the first season goes after a week, but by the second one, which can start at any time, she'll be howling and wailing and calling, desperate to get outside, you'll have male cat piss all over your front door on the outside, her piss over the door and mat on the inside, she'll be grumpy, exhausted, looking like she's in pain and if you don't do it tomorrow (BOOK THE VET TOMORROW!), by day 3 of her second season, which can go on constantly, you'll be offering a thousand pounds to the first person who can make this all stop.
Unless she gets out. Then you'll have kittens, kitten shit, piss, the cost of huge amounts of food, possibly dead kittens, possibly a dead cat, cat flu, FIV, abscesses, and the like - assuming she ever comes back and isn't taken or run over in her search for the nearest unneutered Tomcat.
Book the vet. She needs it.