If she is not spayed and has had access to being outdoors, then she is very likely pregnant. Only time will tell, it will be 63-70 days from when she was outside. If she doesn't get any bigger, you could take her into the vet and request an ultrasound, that will tell you what's going on.
Do you want kittens? If not, she should be spayed now before the halfway mark.
If so, make plans and set aside money to spay her when the kittens are 8 weeks old and do NOT allow her outside or around intact males until after her spay.
Also, you will have a litter of kittens to vet and re-home if she gives birth. There is a great deal of expense and time and effort involved in rearing kittens.