anxiety ridden/reactive pup – need advice 🙁

My dog is turning 3 this year, and she is the sweetest most submissive little thing. She is my very first dog, and I got her at 13 weeks. Though she is so nice and loving to my me, my family, and people she’s known since a puppy, she is not so nice to strangers. She is not aggressive, but she is very scared and anxious around strangers which makes me fear that one day her fear will incite aggression in her as a response. I tried to socialize her the best I could as a puppy, I took her everywhere, let people pet her. She does eventually warm up to new people, it just takes meeting them a few times. While I think some of this anxiety is her breed (springer spaniel)/personality, I am wondering if there is anything I can do to help her be more relaxed around new people. Will dog training help, or make things worse? I just feel overwhelmed and afraid that this is how it will be forever.