These are the two correct answers, IMO. You’ve been told not to come to her house anymore, IME (actual experience with LEOs), once you’ve been told to stay off the property, you can be arrested if you come back. However, there’s no reason why you couldn’t have someone else do it. So there’s that.
The next thing to do would be to send the invoice, along with a letter detailing what the next step is* (small claims, turned over to the police, handed to collections, whatever) in the letter and send it via Certified mail/Return receipt requested. Keep in mind that even if they aren’t home to receive it or outright refuse it, that doesn’t matter. In all the cases I’ve dealt with, you only have to prove that you attempted to get the letter to them, they don’t actually have to receive it. But if it comes back, don’t open it. You’ll need the closed copy if it goes to court.
You might also suggest some alternative to how they can pay such as cash, check or credit card (in which case you’d send them a paypal invoice if you don’t take credit cards). I’ve found that giving people options (especially credit cards), is helpful with hard to collect debts.
But to reiterate, a certified letter with RR, is the next step before anyone ‘official’ is likely to help you out. If the debt it more than $200 or so dollars and it’s easy to show that you did the work, I’m just take them to small claims. Less than that, move on. I don’t know what you do for a living, what you did for her or how you’re related to her WRT her renting the apartment, but going forward it might be worth asking for half upfront (“for materials”) so at least it’s not a total loss when you get stiffed.
*I’ve heard that can be considered extortion, a threat. That is you’re threatening them with something if they don’t give you money, but I don’t know if it’s true. Every time I’ve heard this, they always say, just demand the money and if they don’t give it to you take the next step but don’t phrase it in the form if ‘give me my money or else’. No idea if it’s true, just something I’ve heard.