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Has she been spayed?
If not, this could be classic female in heat symptoms. Females in heat might walk low to the ground, vocalize, be very affectionate and flag their tail to the side.
If you have not had her spayed yet, you will want to do so. If you have already done so, let me know and I'll give more suggestions.
Unfortunately, the only way to ease her pain is to spay her. Cats can be spayed when they are in heat so you might just want to see if you can move her appointment up.
Sometimes is seems like a heat cycle can last forever. Keep in mind that they can go out of heat and then go right back in.
Be SURE to keep her away from males. You don't want her to get pregnant at this age.
If they have been neutered (at least a couple of weeks ago) they cannot get her pregnant but they can still mount and mate with her.
Just keep this in mind when you plan their sleeping quarters!