Now is the time to have your kitten spayed to prevent her from ever having to go into heat.
The symptoms of a kitty in heat are difficult to miss. She will become unusually affectionate, and rub her hind quarters against furniture, other cats, and/or people. She may also vocalize loudly. She will assume a mating position: head down, forelegs bent, rear quarters raised with the tail raised and held to the side of the body. Her rear legs will tread rhythmically, as if walking in place.
Please schedule her for her spay as soon as possible to save her from having to endure this discomfort.