Need advice

Could she come before everyone arrives to do your hair? Or does she have a salon that you could go to?

Sounds like a major red flag. She doesn't sound like a reliable or reasonable person. Would you be able to have her meet you somewhere else to have your hair done? Like a friend or family member's house that don't have as many people?

For starters, don't break the law.

How much is your hair supposed to cost? Is it just you? $400 EXTRA for hair styling for one person is nuts. Also if she doesn't have a salon or phone number and forgot about your trial, she sounds shady. Might just be worth ditching her and forfeiting the costs. If she isn't professional enough to have have a salon or phone number and wants to charge you $400 EXTRA to use an extra site or change your appointment time, I'd be worried she isn't following all the Covid precautions. Having a wedding right now is risky enough with just having the people you love there; I wouldn't risk adding another person particularly if it is someone who has zero emotional value to you and they have just caused stress.

If NJ's regulations only apply to folks indoors, I'd simply make sure there are no more than 10 folks in the house at any given time. Use a different site to get your hair done or have some things going on outdoors.

Also go through your contract. Unless there is a cancelation fee written in there, she really can't charge you any more than you have already paid. Typically the deposit/retainer is held and not refunded if you cancel, but unless you signed a contract that specifically states there are extra charges for canceling you likely won't owe her anything. It might say you pay the full amount or a portion of the full amount or a set fee if you cancel though. If you don't have a contract, well then neither of you are protected and you could probably cancel her, forfeit whatever you have already paid, and walk away.

Who are the ten already in the house? Can anyone leave for a an hour two while she does your hair? Or can anyone come late?