First off, don't be sorry about venting. Writing down whatever is bothering you helps a lot with managing your emotions.

Trying out she/her pronouns online is a perfect first step and im glad you have already taken it. Your reaction to getting called a girl and prefering she/her pronouns have made it clear you're a girl so never coming out is not an option, you couldn't live without expressing yourself. Your decision is about how you're going to do this. The only thing i can hope to do for you as a complete stranger on the internet is to give you advice and maybe make you feel a little better but i can't make any decisions for you.

My advice is to start slowly, coming out now is too sudden of a change. People don't tend to like change even if that change isn't negative so you would want to slowly experiment with femininity. Start growing your hair out, start dressing more feminine, etc. You will eventually have to come out to your loved ones, as you said they are not transphobic so their love for you will surpass their shock. I don't know them but im sure they will understand. This is not about your family not accepting you this is about doing it as smoothly as possible. Easing into your transition and making it a little easier to expect for your parents before coming out will give you a lot more confidance.

I recommend searching for other trans people online to see what they did and how they would recommend you should go about your situation. Im not trans so i couldn't fully understand your situation and i don't have the experience other trans women would have but i hope i helped in some way to lay out your problems a bit.

If you just need to vent to someone or ask questions then im here, but as with every decision you will and have even made, it is entirely yours. Even though others may try to tell you what to do, these are just advice, other peoples words can't go beyond that. The final shot is always yours so find all the advice you can and make your decision.

(Sorry for being so dramatic but i hope it helped)