Yes, it is extremely likely that your kitty is pregnant, following her escape. Unspayed females, once they reach breeding age, will go into heat (or estrus, as it is also called) regularly - as often as every two weeks, until they are either spayed or mate and become pregnant. The loud meowing (also known as "calling") is intended to attract male cats. Since she has stopped calling, I would assume her biological needs have been fulfilled and she has mated.
For more information on mating in cats, read "The Mating Game." And now that your cat is most likely pregnant, there are some important decisions you and your parents need to address. You can find more information on pregnancy and birth in my article, "So Your Cat is Pregnant."
Hope this helps answer your questions!

