Chances are good that if you're accustomed to the fit of that brand's training shoes, its spikes will also work well for you. If that brand doesn't offer spikes, try on as many different models as you possibly can to find the one that fits your feet perfectly. It may surprise you to learn that most of the spikes are very similar in design, weight and traction. The big difference is fit. Try on as many brands as possible.
Some brands fit wider in the forefoot or narrower in the heel.
Most cross-country and track spikes are offered in unisex sizing or just men's. Girls need to pay particular attention to fit. Most girls will need to go down a size to find the ones that fit the best. If you ordinarily wear a size 7 in women's shoes, you'll probably wear a size 5.5-6 in spike sizes. If at all possible, try the shoes on before buying them.