When I was young a neighbour had a Standard Poodle that they sprayed with Bob Martins Anti Mate Spray - that disgusting smell stays with me!
No spray on earth would stop one of my boys from trying it on - and although she is sitting down now, when she is 'ready' she will welcome them from far and wide, pedigree or mongrel, so take extra care. When out she will mark her territory and wee frequently, to attract the boys. She will only be receptive to the males for about two or three days and this could be any time between day 7 and day 30; you will know because she will really flirt with them and stand and flick her tail to one side, particularly if you run your hand down her back. At this time bitches will also try to escape to find a mate, so make sure your fence is secure and doors closed!
If you want to get her spayed, the best time is three months after she has been in season, and although most bitches come in season twice a year, this can vary between every six months to only once a year. They can come in every four months but this is rare and needs checking by a vet.
Another thing to watch for is 'phantom' pregnancy, which can occur about nine weeks after the season (when they would be ready to give birth if they had been mated). They think they have puppies, make a nest and carry toys, often gathering them in their bed licking and squealing at them. You might find your socks missing or tea towels, anything they can mother.
If you ever find your bitch miserable and moping around looking poorly, take her to the vet as there is a serious condition called pyometra (infection of the womb) and usually means they have to be spayed. This can happen at any time, but soon after a season is common.
If you don't want the bother of seasons you can have her injecte a month before she is due, then again after three months, then four months, then every five months until you leave it and