What Lottie says. Also Ebay won't take kindly to her threats - you can report her for that too. Try phoning them and say she has threatened to drag out the case for as long as possible (which she can't do - you still get to escalate at a certain stage, does it have a date on the page when it says you can escalate? That will stand, whatever she does)
Do not communicate further. It's pointless and you do not have to.
Of course ebay will see how ridiculous she is being. It happens a lot sadly.
She's stupid for behaving this way knowing it will get her a negative feedback - by the way do NOT mention feedback to her, there are some funny rules about it and you could get into trouble for 'threatening' it.
please just ignore her now. You are in a good position, don't risk it by getting drawn into an argument and maybe saying the wrong thing in the heat of it.
Check the escalation date and just wait for that and escalate it. And ring them to report her threats and harrassment, if you feel like it.
Don't use the buggy, pack it up again, you already have photos if you need them again, and get it ready to send. Then forget about it till you can escalate.
Have you blocked her from your mobile? If not then do so now.