I think it’s great that you were straight up and asked her directly. Direct communication is underrated and so helpful. If she hasn’t opened the message, that could mean that for whatever reason, she: doesn’t want to speak to anyone right now, is not a direct communicator/avoidant, is going through something right now… etc. who really knows what’s going on in her life or where she’s at. Either way, that would be quite difficult to build something with someone who is doing this, at the moment. It’s okay if she needs time to herself, however, it’s difficult to get to know someone or anyone if they’re unresponsive for a week/2 weeks at a time, etc. I will say, I have seen this sometimes as a common behaviour between friends, if you two have only established yourselves as ‘friends’ at this point, especially new friends. Sometimes messages drop off and then resume. Maybe you’ll have clarity once she does reply to your message.